@article {josey_clearer_2023, title = {A clearer view of Southern Ocean air{\textendash}sea interaction using surface heat flux asymmetry}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {381}, number = {2249}, year = {2023}, note = {Publisher: Royal Society}, month = {may}, pages = {20220067}, abstract = {Progress in understanding Southern Ocean heat exchange and wind forcing is discussed and new results presented. These include a metric of the zonal asymmetry between surface ocean heat gain in the Atlantic/Indian sector and heat loss in the Pacific sector. The asymmetry arises from an intersector variation in the humidity gradient between the sea surface and near-surface atmosphere. This gradient increases by 60\% in the Pacific sector enabling a 20 Wm-2 stronger latent heat loss compared with the Atlantic/Indian sector. The new metric is used for intercomparison of atmospheric reanalyses and CMIP6 climate simulations. CMIP6 has weaker Atlantic/Indian sector heat gain compared with the reanalyses primarily due to Indian Ocean sector differences. The potential for surface flux buoys to provide an observation-based counterpart to the asymmetry metric is explored. Over the past decade, flux buoys have been deployed at two sites (south of Tasmania and upstream of Drake Passage). The data record provided by these moorings is assessed and an argument developed for a third buoy to sample the Atlantic/Indian sector of the asymmetry metric. To close, we assess evidence that the main westerly wind belt has strengthened and moved southward in recent decades using the ERA5 reanalysis. This article is part of a discussion meeting issue {\textquoteright}Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities{\textquoteright}.}, keywords = {air{\textendash}sea heat flux, Southern Ocean, wind stress}, doi = {10.1098/rsta.2022.0067}, url = {https://royalsocietypublishing.org/doi/full/10.1098/rsta.2022.0067}, author = {Josey, Simon A. and Grist, Jeremy P. and Mecking, Jennifer V. and Moat, Ben I. and Schulz, Eric} } @article {meijers_finale_2023, title = {Finale: impact of the ORCHESTRA/ENCORE programmes on Southern Ocean heat and carbon understanding}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {381}, number = {2249}, year = {2023}, note = {Publisher: Royal Society}, month = {may}, pages = {20220070}, abstract = {The 5-year Ocean Regulation of Climate by Heat and Carbon Sequestration and Transports (ORCHESTRA) programme and its 1-year extension ENCORE (ENCORE is the National Capability ORCHESTRA Extension) was an approximately 11-million-pound programme involving seven UK research centres that finished in March 2022. The project sought to radically improve our ability to measure, understand and predict the exchange, storage and export of heat and carbon by the Southern Ocean. It achieved this through a series of milestone observational campaigns in combination with model development and analysis. Twelve cruises in the Weddell Sea and South Atlantic were undertaken, along with mooring, glider and profiler deployments and aircraft missions, all contributing to measurements of internal ocean and air{\textendash}sea heat and carbon fluxes. Numerous forward and adjoint numerical experiments were developed and supported by the analysis of coupled climate models. The programme has resulted in over 100 peer-reviewed publications to date as well as significant impacts on climate assessments and policy and science coordination groups. Here, we summarize the research highlights of the programme and assess the progress achieved by ORCHESTRA/ENCORE and the questions it raises for the future. This article is part of a discussion meeting issue {\textquoteleft}Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities{\textquoteright}.}, keywords = {climate, ocean carbon, ocean circulation, ocean heat, ocean{\textendash}atmosphere fluxes, Southern Ocean}, doi = {10.1098/rsta.2022.0070}, url = {https://royalsocietypublishing.org/doi/full/10.1098/rsta.2022.0070}, author = {Meijers, Andrew J. S. and Meredith, Michael P. and Shuckburgh, Emily F. and Kent, Elizabeth C. and Munday, David R. and Firing, Yvonne L. and King, Brian and Smyth, Tim J. and Leng, Melanie J. and George Nurser, A. J. and Hewitt, Helene T. and Povl Abrahamsen, E. and Weiss, Alexandra and Yang, Mingxi and Bell, Thomas G. and Alexander Brearley, J. and Boland, Emma J. D. and Jones, Daniel C. and Josey, Simon A. and Owen, Robyn P. and Grist, Jeremy P. and Blaker, Adam T. and Biri, Stavroula and Yelland, Margaret J. and Pimm, Ciara and Zhou, Shenjie and Harle, James and Cornes, Richard C.} } @article {tamsitt_new_2023, title = {New insights into air-sea fluxes and their role in Subantarctic Mode Water formation}, journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences}, volume = {381}, number = {2249}, year = {2023}, note = {Publisher: Royal Society}, month = {may}, pages = {20220066}, abstract = {The formation of Subantarctic Mode Water SAMW in the Southern Ocean plays a key role in the global oceanic uptake and storage of anthropogenic heat and carbon. Wintertime ocean surface heat loss is a dominant driver of Subantarctic Mode Water formation and variability, but wintertime air-sea flux observations in the Southern Ocean are extremely sparse. Recent advances in our understanding of the role of air-sea fluxes in Subantarctic Mode Water Formation from novel ocean observations are summarized here, particularly the role of synoptic atmospheric extreme events, and the drivers of interannual variations in SAMW. These advances in understanding have important implications for variability in Southern Ocean heat and carbon uptake, and can inform future Southern Ocean observing system design. This article is part of a discussion meeting issue {\textquoteleft}Heat and carbon uptake in the Southern Ocean: the state of the art and future priorities{\textquoteright}.}, keywords = {air-sea fluxes, mooring time series, ocean observing, Subantarctic Mode Water, water mass formation}, doi = {10.1098/rsta.2022.0066}, url = {https://royalsocietypublishing.org/doi/full/10.1098/rsta.2022.0066}, author = {Tamsitt, V.} } @mastersthesis {ainsworth_carbon_2022, title = {Carbon - trace metal interactions in the oceanic twilight zone}, volume = {Doctor of Philosophy}, year = {2022}, month = {05/2022}, school = {University of Southampton}, type = {PhD}, abstract = {Marine microbes are an important control on carbon (C) sequestration depth and biogeochemical cycling of nutrients and trace metals in the global ocean. The biological carbon pump (BCP) is the set of processes by which inorganic carbon (CO$_\textrm2$) (along with nutrients and trace metals) is fixed into organic matter via photosynthesis by autotrophic phytoplankton and the C, nutrients and trace metals sequestered away from the atmosphere generally by transport into the deep ocean. Most (\textasciitilde80 \%) of the organic C produced by autotrophic phytoplankton is remineralised (returned to the dissolved inorganic inventory from the particulate organic form) in the surface ocean and the inorganic CO$_\textrm2$ is available for release back into the atmosphere. The depth at which remineralisation occurs is important, as the deeper the remineralisation depth of the C the increased likelihood of long term storage in the deep water and sediment. The sequestration of C is primarily dependent on flux attenuation and remineralisation of organic matter in the mesopelagic or {\textquoteleft}twilight{\textquoteright} zone (100-1000 m), where much of the downward particle flux is attenuated via zooplankton and bacterial respiration, replenishing dissolved nutrients and trace metals back into the water column. Understanding the controls on the BCP in the twilight zone is important to understand the transfer efficiency of C sequestration and the regulation of atmospheric CO$_\textrm2$. Oceanic regions such as the Southern Ocean have inefficient BCPs as the phytoplankton are unable to fully utilise available nutrients, restricting their growth and drawdown of C due to limited access to micronutrients such as iron (Fe). Iron is a scare resource in these regions and low concentrations of bioavailable Fe exert significant controls on global phytoplankton productivity, species composition and therefore ecosystem structure and the C cycle. Iron is not only an important micronutrient for phytoplankton growth but also for heterotrophic bacteria, limiting bacterial secondary production and abundance. Two focused and inter-related processes which influence Fe cycling and consequently C cycling in the mesopelagic were investigated. Firstly, differentiating the biotic and abiotic factors on Fe cycling in the twilight zone and the (de-) coupling of Fe and macronutrients at depth. Secondly, to investigate Fe and C (co-) limitation of mesopelagic bacteria. This researched performed shipboard experiments and subsequent laboratory work to evaluate the relative remineralisation rates of C, Fe and silica (Si) from live and detrital phytoplankton cells resuspended in upper mesopelagic waters. Iron consistently transferred from the particulate fraction into the dissolved fraction from both live and detrital cells, this transfer was dominated by the abiotic movement of extracellular adsorbed particulate iron into the dissolved fraction (de- absorption). The live phytoplankton cells remained viable throughout the incubations and continued to respire C whilst the detrital cells potentially leaked dissolved organic C which was subsequently taken up and respired by bacteria with minimal secondary bacterial production. Limited dissolution of Si occurred from the live viable cells with the detrital cells showing more Si dissolution potential. The remineralisation length scales of Fe, C and Si were thus decoupled in the upper mesopelagic as Fe resulted in the shortest remineralisation length scale due the abiotic transfer of extracellular Fe into the dissolved pool, which could resupply biota potentially alleviating Fe limitation. Intracellular pools of Fe (along with C and Si) would be exported to deeper depths with a slow remineralisation rate if processes such as grazing or cell lysis do not act to break cells up and speed up remineralisation processes. Heterotrophic bacterial production was Fe and C (co-) limited in the mesopelagic above the ferricline. An increase in cell abundance of very large high nucleic bacteria when combined Fe and C were added to mesopelagic waters from 150 and 500 m supported a large (1-2 order of magnitude) increase in bacterial production indicating the (co-) limitation of a sub-population of the free-living bacteria at depth. The controls on ferricline depth and mesopelagic standing stocks of Fe (from winter mixing, scavenging, Fe associated with sinking material and the de-absorption of Fe into the water column) will be important in determining the extent of ocean Fe C (co-) limitation of mesopelagic bacterial growth and production and will be a driver in bacterial community composition at depth. Nutrient limitation in the mesopelagic bacteria has potentially important consequences if it also reduces the overall rate of remineralisation and thus both generates a potential reinforcing feedback on the maintenance of a deep ferricline and increases the remineralisation depth and hence long-term storage of carbon in the ocean.}, url = {https://eprints.soton.ac.uk/467733/}, author = {Ainsworth, Joanna Jane} } @article {cerovecki_impact_2022, title = {Impact of downward longwave radiative deficits on Antarctic sea-ice extent predictability during the sea ice growth period}, journal = {Environmental Research Letters}, volume = {17}, number = {8}, year = {2022}, note = {Place: Bristol Publisher: IOP Publishing Ltd WOS:000827243700001}, pages = {084008}, abstract = {Forecasting Antarctic atmospheric, oceanic, and sea ice conditions on subseasonal to seasonal scales remains a major challenge. During both the freezing and melting seasons current operational ensemble forecasting systems show a systematic overestimation of the Antarctic sea-ice edge location. The skill of sea ice cover prediction is closely related to the accuracy of cloud representation in models, as the two are strongly coupled by cloud radiative forcing. In particular, surface downward longwave radiation (DLW) deficits appear to be a common shortcoming in atmospheric models over the Southern Ocean. For example, a recent comparison of ECMWF reanalysis 5th generation (ERA5) global reanalysis with the observations from McMurdo Station revealed a year-round deficit in DLW of approximately 50 Wm(-2) in marine air masses due to model shortages in supercooled cloud liquid water. A comparison with the surface DLW radiation observations from the Ocean Observatories Initiative mooring in the South Pacific at 54.08 degrees S, 89.67 degrees W, for the time period January 2016-November 2018, confirms approximately 20 Wm(-2) deficit in DLW in ERA5 well north of the sea-ice edge. Using a regional ocean model, we show that when DLW is artificially increased by 50 Wm(-2) in the simulation driven by ERAS atmospheric forcing, the predicted sea ice growth agrees much better with the observations. A wide variety of sensitivity tests show that the anomalously large, predicted sea-ice extent is not due to limitations in the ocean model and that by implication the cause resides with the atmospheric forcing.}, keywords = {Antarctic subseasonal sea ice predictability, coupled modeling of the Southern Ocean, downward longwave radiation deficit, model, ocean, polar weather research, shelf}, issn = {1748-9326}, doi = {10.1088/1748-9326/ac7d66}, url = {https://iopscience.iop.org/article/10.1088/1748-9326/ac7d66}, author = {Cerovecki, Ivana and Sun, Rui and Bromwich, David H. and Zou, Xun and Mazloff, Matthew R. and Wang, Sheng-Hung} } @article {RN207, title = {Wind, waves, and surface currents in the Southern Ocean: observations from the Antarctic Circumnavigation Expedition}, journal = {Earth System Science Data}, volume = {13}, number = {3}, year = {2021}, pages = {1189-1209}, type = {Journal Article}, abstract = { The Southern Ocean has a profound impact on the Earth{\textquoteright}s climate system. Its strong winds, intense currents, and fierce waves are critical components of the air{\textendash}sea interface and contribute to absorbing, storing, and releasing heat, moisture, gases, and momentum. Owing to its remoteness and harsh environment, this region is significantly undersampled, hampering the validation of prediction models and large-scale observations from satellite sensors. Here, an unprecedented data set of simultaneous observations of winds, surface currents, and ocean waves is presented, to address the scarcity of in situ observations in the region {\textendash} https://doi.org/10.26179/5ed0a30aaf764 (Alberello et al., 2020c) and https://doi.org/10.26179/5e9d038c396f2 (Derkani et al., 2020). Records were acquired underway during the Antarctic Circumnavigation Expedition (ACE), which went around the Southern Ocean from December 2016 to March 2017 (Austral summer). Observations were obtained with the wave and surface current monitoring system WaMoS-II, which scanned the ocean surface around the vessel using marine radars. Measurements were assessed for quality control and compared against available satellite observations. The data set is the most extensive and comprehensive collection of observations of surface processes for the Southern Ocean and is intended to underpin improvements of wave prediction models around Antarctica and research of air{\textendash}sea interaction processes, including gas exchange and dynamics of sea spray aerosol particles. The data set has further potentials to support theoretical and numerical research on lower atmosphere, air{\textendash}sea interface, and upper-ocean processes.}, doi = {10.5194/essd-13-1189-2021}, url = {https://app.dimensions.ai/details/publication/pub.1136590412 https://essd.copernicus.org/articles/13/1189/2021/essd-13-1189-2021.pdf}, author = {Derkani, Marzieh H. and Alberello, Alberto and Nelli, Filippo and Bennetts, Luke G. and Hessner, Katrin G. and MacHutchon, Keith and Reichert, Konny and Aouf, Lotfi and Khan, Salman and Toffoli, Alessandro} } @article {RN177, title = {Deep Learning for Predicting Significant Wave Height From Synthetic Aperture Radar}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, volume = {PP}, number = {99}, year = {2020}, pages = {1-9}, type = {Journal Article}, abstract = {The Sentinel-1 satellites equipped with synthetic aperture radars (SARs) provide near-global coverage of the world{\textquoteright}s oceans every six days. We curate a data set of collocations between SAR and altimeter satellites and investigate the use of deep learning to predict significant wave height from SAR. While previous models for predicting geophysical quantities from SAR rely heavily on feature-engineering, our approach learns directly from low-level image cross-spectra. Training on collocations from 2015 to 2017, we demonstrate on test data from 2018 that deep learning reduces the state-of-the-art root mean squared error by 50\%, from 0.6 to 0.3 m when compared to altimeter data. Furthermore, we isolate the contributions of different features to the model performance.}, keywords = {Data models, Modulation, Satellites, Sea measurements, Sea surface, Synthetic aperture radar}, doi = {10.1109/tgrs.2020.3003839}, url = {https://app.dimensions.ai/details/publication/pub.1129457664}, author = {Quach, Brandon and Glaser, Yannik and Stopa, Justin Edward and Mouche, Alexis Aurelien and Sadowski, Peter} } @article {RN174, title = {Estimating Southern Ocean Storm Positions With Seismic Observations}, journal = {Journal of Geophysical Research Oceans}, volume = {125}, number = {4}, year = {2020}, type = {Journal Article}, abstract = {Surface winds from Southern Ocean cyclones generate large waves that travel over long distances (>1,000 km). Wave generation regions are often colocated with enhanced air-sea fluxes and upper ocean mixing. Ocean wave spectra contain information about storm wind speed, fetch size, and intensity at their generation site. Two years of seismic observations on the Ross Ice shelf, combined with modern optimization (machine learning) techniques, are used to trace the origins of wave events in the Southern Ocean with an accuracy of {\textpm}110 km and {\textpm}2 hr from a hypothetical point source. The observed spectral energy attenuated within sea ice and in the ice shelf but retains characteristics that can be compared to parametric wave models. Comparison with the Modern-Era Retrospective Analysis for Research and Applications, Version 2, and ERA5 reanalyses suggests that less than 45\% of ocean swell events can be associated with individual Southern Ocean storms, while the majority of the observed wave events cannot be matched with Southern Ocean high wind events. Reanalysis cyclones and winds are often displaced by about 350 km or 10 hr in Modern-Era Retrospective Analysis for Research and Applications, Version 2, and ERA5 compared to the most likely positions inferred from the seismic spectra. This high fraction of displaced storms in reanalysis products over the South Pacific can be explained by the limited availability of remote sensing observations, primarily caused by the presence of sea ice. Deviation of wave rays from their great circle path by wave-current interaction plays a minor role.}, doi = {10.1029/2019jc015898}, url = {https://app.dimensions.ai/details/publication/pub.1126055069 https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2019JC015898}, author = {Hell, Momme C. and Gille, Sarah T. and Cornuelle, Bruce D. and Miller, Arthur J. and Bromirski, Peter D. and Crawford, Alex D.} } @article {RN153, title = {Mooring Observations of Air-Sea Heat Fluxes in Two Subantarctic Mode Water Formation Regions}, journal = {Journal of Climate}, volume = {33}, number = {7}, year = {2020}, pages = {2757-2777}, type = {Journal Article}, abstract = {Wintertime surface ocean heat loss is the key process driving the formation of Subantarctic Mode Water (SAMW), but there are few direct observations of heat fluxes, particularly during winter. The Ocean Observatories Initiative (OOI) Southern Ocean mooring in the southeast Pacific Ocean and the Southern Ocean Flux Station (SOFS) in the southeast Indian Ocean provide the first concurrent, multiyear time series of air{\textendash}sea fluxes in the Southern Ocean from two key SAMW formation regions. In this work we compare drivers of wintertime heat loss and SAMW formation by comparing air{\textendash}sea fluxes and mixed layers at these two mooring locations. A gridded Argo product and the ERA5 reanalysis product provide temporal and spatial context for the mooring observations. Turbulent ocean heat loss is on average 1.5 times larger in the southeast Indian (SOFS) than in the southeast Pacific (OOI), with stronger extreme heat flux events in the southeast Indian leading to larger cumulative winter ocean heat loss. Turbulent heat loss events in the southeast Indian (SOFS) occur in two atmospheric regimes (cold air from the south or dry air circulating via the north), while heat loss events in the southeast Pacific (OOI) occur in a single atmospheric regime (cold air from the south). On interannual time scales, wintertime anomalies in net heat flux and mixed layer depth (MLD) are often correlated at the two sites, particularly when wintertime MLDs are anomalously deep. This relationship is part of a larger basin-scale zonal dipole in heat flux and MLD anomalies present in both the Indian and Pacific basins, associated with anomalous meridional atmospheric circulation.}, keywords = {Atmosphere-ocean interaction, Buoy observations, Heat budgets/fluxes, Oceanic mixed layer, Southern Ocean, Water masses/storage}, issn = {0894-8755}, doi = {10.1175/JCLI-D-19-0653.1}, author = {Tamsitt, V. and Cerovecki, I. and Josey, S. A. and Gille, S. T. and Schulz, E.} } @article {RN188, title = {Optimizing Mooring Placement to Constrain Southern Ocean Air-Sea Fluxes}, journal = {Journal of Atmospheric and Oceanic Technology}, volume = {37}, number = {8}, year = {2020}, pages = {1365-1385}, type = {Journal Article}, abstract = {Proposals from multiple nations to deploy air{\textendash}sea flux moorings in the Southern Ocean have raised the question of how to optimize the placement of these moorings in order to maximize their utility, both as contributors to the network of observations assimilated in numerical weather prediction and also as a means to study a broad range of processes driving air{\textendash}sea fluxes. This study, developed as a contribution to the Southern Ocean Observing System (SOOS), proposes criteria that can be used to determine mooring siting to obtain best estimates of net air{\textendash}sea heat flux (Qnet). Flux moorings are envisioned as one component of a multiplatform observing system, providing valuable in situ point time series measurements to be used alongside satellite data and observations from autonomous platforms and ships. Assimilating models (e.g., numerical weather prediction and reanalysis products) then offer the ability to synthesize the observing system and map properties between observations. This paper develops a framework for designing mooring array configurations to maximize the independence and utility of observations. As a test case, within the meridional band from 35{\textdegree} to 65{\textdegree}S we select eight mooring sites optimized to explain the largest fraction of the total variance (and thus to ensure the least variance of residual components) in the area south of 20{\textdegree}S. Results yield different optimal mooring sites for low-frequency interannual heat fluxes compared with higher-frequency subseasonal fluxes. With eight moorings, we could explain a maximum of 24.6\% of high-frequency Qnet variability or 44.7\% of low-frequency Qnet variability.}, keywords = {Buoy observations, In situ atmospheric observations, In situ oceanic observations, Southern Ocean}, issn = {0739-0572}, doi = {10.1175/JTECH-D-19-0203.1}, author = {Wei, Y. Z. and Gille, S. T. and Mazloff, M. R. and Tamsitt, V. and Swart, S. and Chen, D. K. and Newman, L.} } @article {RN70, title = {Calibration of the Normalized Radar Cross Section for Sentinel-1 Wave Mode}, journal = {IEEE Transactions on Geoscience and Remote Sensing}, volume = {57}, number = {3}, year = {2019}, pages = {1514-1522}, type = {Journal Article}, abstract = {Sentinel-1 (S-1) is a two-satellite constellation for continuity of operational synthetic aperture radar (SAR) observations. Wave mode (WV) is the default mode over open ocean for S-1 to monitor global ocean waves and wind field. Therefore, proper radiometric calibration is essential to accurately infer these geophysical quantities. Based on the global data set acquired by S-1A WV, assessment of normalized radar cross section (NRCS) is carried out through comparison with CMOD5.N predictions over open ocean. The calibration accuracy quantified by NRCS residuals between SAR measurements and CMOD5.N demonstrates distinct features for two incidence angles (23.8{\textdegree} and 36.8{\textdegree}). Particularly, NRCS at 23.8{\textdegree} is overall consistent with CMOD5.N, while NRCS at 36.8{\textdegree} displays great deviation. Two recalibration methods are then implemented by examining the backscattering profile over Amazon rain forest and ocean calibration. Both methods show the necessity for recalibration and obtain comparable correction factors for WV1 and WV2, respectively. The NRCS residuals by applying both methods are significantly reduced toward zero. By comparison, ocean calibration is more efficient and practical to implement.}, keywords = {Calibration, Histograms, Oceans, Radiometry, Rain, Synthetic aperture radar, Wind speed}, issn = {0196-2892}, doi = {10.1109/TGRS.2018.2867035}, author = {Li, H. and Mouche, A. and Stopa, J. E. and Chapron, B.} } @article {RN148, title = {Constraining Southern Ocean Air-Sea-Ice Fluxes Through Enhanced Observations}, journal = {Frontiers in Marine Science}, volume = {6}, year = {2019}, pages = {421}, type = {Journal Article}, abstract = {Air-sea and air-sea-ice fluxes in the Southern Ocean play a critical role in global climate through their impact on the overturning circulation and oceanic heat and carbon uptake. The challenging conditions in the Southern Ocean have led to sparse spatial and temporal coverage of observations. This has led to a {\textquotedblleft}knowledge gap{\textquotedblright} that increases uncertainty in atmosphere and ocean dynamics and boundary-layer thermodynamic processes, impeding improvements in weather and climate models. Improvements will require both process-based research to understand the mechanisms governing air-sea exchange and a significant expansion of the observing system. This will improve flux parameterizations and reduce uncertainty associated with bulk formulae and satellite observations. Improved estimates spanning the full Southern Ocean will need to take advantage of ships, surface moorings, and the growing capabilities of autonomous platforms with robust and miniaturized sensors. A key challenge is to identify observing system sampling requirements. This requires models, Observing System Simulation Experiments (OSSEs), and assessments of the specific spatial-temporal accuracy and resolution required for priority science and assessment of observational uncertainties of the mean state and direct flux measurements. Year-round, high-quality, quasi-continuous in situ flux measurements and observations of extreme events are needed to validate, improve and characterize uncertainties in blended reanalysis products and satellite data as well as to improve parameterizations. Building a robust observing system will require community consensus on observational methodologies, observational priorities, and effective strategies for data management and discovery.}, keywords = {air-sea/air-sea-ice fluxes, climate, ocean{\textendash}atmosphere interaction, ocean{\textendash}ice interaction, Southern Ocean}, issn = {2296-7745}, doi = {10.3389/fmars.2019.00421}, url = {https://www.frontiersin.org/article/10.3389/fmars.2019.00421}, author = {Swart, Sebastiaan and Gille, Sarah T. and Delille, Bruno and Josey, Simon and Mazloff, Matthew and Newman, Louise and Thompson, Andrew F. and Thomson, Jim and Ward, Brian and du Plessis, Marcel D. and Kent, Elizabeth C. and Girton, James and Gregor, Luke and Heil, Petra and Hyder, Patrick and Pezzi, Luciano Ponzi and de Souza, Ronald Buss and Tamsitt, Veronica and Weller, Robert A. and Zappa, Christopher J.} } @article {RN108, title = {Integrated Observations of Global Surface Winds, Currents, and Waves: Requirements and Challenges for the Next Decade}, journal = {Frontiers in Marine Science}, volume = {6}, year = {2019}, pages = {425}, type = {Journal Article}, abstract = {Ocean surface winds, currents, and waves play a crucial role in exchanges of momentum, energy, heat, freshwater, gases, and other tracers between the ocean, atmosphere, and ice. Despite surface waves being strongly coupled to the upper ocean circulation and the overlying atmosphere, efforts to improve ocean, atmospheric, and wave observations and models have evolved somewhat independently. From an observational point of view, community efforts to bridge this gap have led to proposals for satellite Doppler oceanography mission concepts, which could provide unprecedented measurements of absolute surface velocity and directional wave spectrum at global scales. This paper reviews the present state of observations of surface winds, currents, and waves, and it outlines observational gaps that limit our current understanding of coupled processes that happen at the air-sea-ice interface. A significant challenge for the coming decade of wind, current, and wave observations will come in combining and interpreting measurements from (a) wave-buoys and high-frequency radars in coastal regions, (b) surface drifters and wave-enabled drifters in the open-ocean, marginal ice zones, and wave-current interaction {\textquotedblleft}hot-spots,{\textquotedblright} and (c) simultaneous measurements of absolute surface currents, ocean surface wind vector, and directional wave spectrum from Doppler satellite sensors.}, keywords = {absolute surface velocity, air-sea interactions, Doppler oceanography from space, ocean surface winds, surface waves}, issn = {2296-7745}, doi = {10.3389/fmars.2019.00425}, url = {https://www.frontiersin.org/article/10.3389/fmars.2019.00425}, author = {Villas B{\^o}as, Ana B. and Ardhuin, Fabrice and Ayet, Alex and Bourassa, Mark A. and Brandt, Peter and Chapron, Betrand and Cornuelle, Bruce D. and Farrar, J. T. and Fewings, Melanie R. and Fox-Kemper, Baylor and Gille, Sarah T. and Gommenginger, Christine and Heimbach, Patrick and Hell, Momme C. and Li, Qing and Mazloff, Matthew R. and Merrifield, Sophia T. and Mouche, Alexis and Rio, Marie H. and Rodriguez, Ernesto and Shutler, Jamie D. and Subramanian, Aneesh C. and Terrill, Eric J. and Tsamados, Michel and Ubelmann, Clement and van Sebille, Erik} } @article {RN111, title = {Polar Ocean Observations: A Critical Gap in the Observing System and Its Effect on Environmental Predictions From Hours to a Season}, journal = {Frontiers in Marine Science}, volume = {6}, year = {2019}, pages = {429}, type = {Journal Article}, abstract = {There is a growing need for operational oceanographic predictions in both the Arctic and Antarctic polar regions. In the former, this is driven by a declining ice cover accompanied by an increase in maritime traffic and exploitation of marine resources. Oceanographic predictions in the Antarctic are also important, both to support Antarctic operations and also to help elucidate processes governing sea ice and ice shelf stability. However, a significant gap exists in the ocean observing system in polar regions, compared to most areas of the global ocean, hindering the reliability of ocean and sea ice forecasts. This gap can also be seen from the spread in ocean and sea ice reanalyses for polar regions which provide an estimate of their uncertainty. The reduced reliability of polar predictions may affect the quality of various applications including search and rescue, coupling with numerical weather and seasonal predictions, historical reconstructions (reanalysis), aquaculture and environmental management including environmental emergency response. Here, we outline the status of existing near-real time ocean observational efforts in polar regions, discuss gaps, and explore perspectives for the future. Specific recommendations include a renewed call for open access to data, especially real-time data, as a critical capability for improved sea ice and weather forecasting and other environmental prediction needs. Dedicated efforts are also needed to make use of additional observations made as part of the Year of Polar Prediction (YOPP; 2017{\textendash}2019) to inform optimal observing system design. To provide a polar extension to the Argo network, it is recommended that a network of ice-borne sea ice and upper-ocean observing buoys be deployed and supported operationally in ice-covered areas together with autonomous profiling floats and gliders (potentially with ice detection capability) in seasonally ice covered seas. Finally, additional efforts to better measure and parameterize surface exchanges in polar regions are much needed to improve coupled environmental prediction.}, keywords = {air-sea-ice fluxes, forecasting, ocean data assimilation, ocean modeling, operational oceanography, polar observations, sea ice, YOPP}, issn = {2296-7745}, doi = {10.3389/fmars.2019.00429}, url = {https://www.frontiersin.org/article/10.3389/fmars.2019.00429}, author = {Smith, Gregory C. and Allard, Richard and Babin, Marcel and Bertino, Laurent and Chevallier, Matthieu and Corlett, Gary and Crout, Julia and Davidson, Fraser and Delille, Bruno and Gille, Sarah T. and Hebert, David and Hyder, Patrick and Intrieri, Janet and Lagunas, Jos{\'e} and Larnicol, Gilles and Kaminski, Thomas and Kater, Belinda and Kauker, Frank and Marec, Claudie and Mazloff, Matthew and Metzger, E. Joseph and Mordy, Calvin and O{\textquoteright}Carroll, Anne and Olsen, Steffen M. and Phelps, Michael and Posey, Pamela and Prandi, Pierre and Rehm, Eric and Reid, Phillip and Rigor, Ignatius and Sandven, Stein and Shupe, Matthew and Swart, Sebastiaan and Smedstad, Ole Martin and Solomon, Amy and Storto, Andrea and Thibaut, Pierre and Toole, John and Wood, Kevin and Xie, Jiping and Yang, Qinghua and Group, the Wwrp P. P. P. Steering} } @article {RN118, title = {Southern Ocean Biogeochemical Float Deployment Strategy, With Example From the Greenwich Meridian Line (GO-SHIP A12)}, journal = {Journal of Geophysical Research: Oceans}, volume = {124}, number = {1}, year = {2019}, pages = {403-431}, type = {Journal Article}, abstract = {Biogeochemical Argo floats, profiling to 2,000-m depth, are being deployed throughout the Southern Ocean by the Southern Ocean Carbon and Climate Observations and Modeling program (SOCCOM). The goal is 200 floats by 2020, to provide the first full set of annual cycles of carbon, oxygen, nitrate, and optical properties across multiple oceanographic regimes. Building from no prior coverage to a sparse array, deployments are based on prior knowledge of water mass properties, mean frontal locations, mean circulation and eddy variability, winds, air-sea heat/freshwater/carbon exchange, prior Argo trajectories, and float simulations in the Southern Ocean State Estimate and Hybrid Coordinate Ocean Model (HYCOM). Twelve floats deployed from the 2014{\textendash}2015 Polarstern cruise from South Africa to Antarctica are used as a test case to evaluate the deployment strategy adopted for SOCCOM{\textquoteright}s 20 deployment cruises and 126 floats to date. After several years, these floats continue to represent the deployment zones targeted in advance: (1) Weddell Gyre sea ice zone, observing the Antarctic Slope Front, and a decadally-rare polynya over Maud Rise; (2) Antarctic Circumpolar Current (ACC) including the topographically steered Southern Zone chimney where upwelling carbon/nutrient-rich deep waters produce surprisingly large carbon dioxide outgassing; (3) Subantarctic and Subtropical zones between the ACC and Africa; and (4) Cape Basin. Argo floats and eddy-resolving HYCOM simulations were the best predictors of individual SOCCOM float pathways, with uncertainty after 2 years of order 1,000 km in the sea ice zone and more than double that in and north of the ACC.}, issn = {2169-9275}, doi = {10.1029/2018JC014059}, url = {https://doi.org/10.1029/2018JC014059}, author = {Talley, L. D. and Rosso, I. and Kamenkovich, I. and Mazloff, M. R. and Wang, J. and Boss, E. and Gray, A. R. and Johnson, K. S. and Key, R. M. and Riser, S. C. and Williams, N. L. and Sarmiento, J. L.} } @article {RN107, title = {Waves and Swells in High Wind and Extreme Fetches, Measurements in the Southern Ocean}, journal = {Frontiers in Marine Science}, volume = {6}, year = {2019}, pages = {361}, type = {Journal Article}, abstract = {The generation and evolution of ocean waves by wind is one of the most complex phenomena in geophysics, and is of great practical significance. Predictive capabilities of respective wave models, however, are impaired by lack of field in situ observations, particularly in extreme Metocean conditions. The paper outlines and highlights important gaps in understanding the Metocean processes and suggests a major observational program in the Southern Ocean. This large, but poorly investigated part of the World Ocean is home to extreme weather around the year. The observational network would include distributed system of buoys (drifting and stationary) and autonomous surface vehicles (ASV), intended for measurements of waves and air-sea fluxes in the Southern Ocean. It would help to resolve the issues of limiting fetches, extreme Extra-Tropical cyclones, swell propagation and attenuation, wave-current interactions, and address the topics of wave-induced dispersal of floating objects, wave-ice interactions in the Marginal Ice Zone, Metocean climatology and its connection with the global climate.}, keywords = {air-sea and air-sea-land interaction processes, extra-tropical anticyclones, extreme wave, wave fetch, wind wave and swell}, issn = {2296-7745}, doi = {10.3389/fmars.2019.00361}, author = {Babanin, Alexander V. and Rogers, W. Erick and de Camargo, Ricardo and Doble, Martin and Durrant, Tom and Filchuk, Kirill and Ewans, Kevin and Hemer, Mark and Janssen, Tim and Kelly-Gerreyn, Boris and MacHutchon, Keith and McComb, Peter and Qiao, Fangli and Schulz, Eric and Skvortsov, Alex and Thomson, Jim and Vichi, Marcello and Violante-Carvalho, Nelson and Wang, David and Waseda, Takuji and Williams, Greg and Young, Ian R.} } @article {RN32, title = {Detection of climate change-driven trends in phytoplankton phenology}, journal = {Glob Chang Biol}, volume = {24}, number = {1}, year = {2018}, pages = {e101-e111}, type = {Journal Article}, abstract = {The timing of the annual phytoplankton spring bloom is likely to be altered in response to climate change. Quantifying that response has, however, been limited by the typically coarse temporal resolution (monthly) of global climate models. Here, we use higher resolution model output (maximum 5 days) to investigate how phytoplankton bloom timing changes in response to projected 21st century climate change, and how the temporal resolution of data influences the detection of long-term trends. We find that bloom timing generally shifts later at mid-latitudes and earlier at high and low latitudes by ~5 days per decade to 2100. The spatial patterns of bloom timing are similar in both low (monthly) and high (5 day) resolution data, although initiation dates are later at low resolution. The magnitude of the trends in bloom timing from 2006 to 2100 is very similar at high and low resolution, with the result that the number of years of data needed to detect a trend in phytoplankton phenology is relatively insensitive to data temporal resolution. We also investigate the influence of spatial scales on bloom timing and find that trends are generally more rapidly detectable after spatial averaging of data. Our results suggest that, if pinpointing the start date of the spring bloom is the priority, the highest possible temporal resolution data should be used. However, if the priority is detecting long-term trends in bloom timing, data at a temporal resolution of 20 days are likely to be sufficient. Furthermore, our results suggest that data sources which allow for spatial averaging will promote more rapid trend detection.}, issn = {1365-2486 (Electronic) 1354-1013 (Linking)}, doi = {10.1111/gcb.13886}, url = {https://www.ncbi.nlm.nih.gov/pubmed/28871605}, author = {Henson, S. A. and Cole, H. S. and Hopkins, J. and Martin, A. P. and Yool, A.} } @article {RN40, title = {Episodic Southern Ocean Heat Loss and Its Mixed Layer Impacts Revealed by the Farthest South Multiyear Surface Flux Mooring}, journal = {Geophysical Research Letters}, volume = {45}, number = {10}, year = {2018}, pages = {5002-5010}, type = {Journal Article}, abstract = {The Ocean Observatories Initiative air-sea flux mooring deployed at 54.08{\textdegree}S, 89.67{\textdegree}W, in the southeast Pacific sector of the Southern Ocean, is the farthest south long-term open ocean flux mooring ever deployed. Mooring observations (February 2015 to August 2017) provide the first in situ quantification of annual net air-sea heat exchange from one of the prime Subantarctic Mode Water formation regions. Episodic turbulent heat loss events (reaching a daily mean net flux of -294 W/m2) generally occur when northeastward winds bring relatively cold, dry air to the mooring location, leading to large air-sea temperature and humidity differences. Wintertime heat loss events promote deep mixed layer formation that lead to Subantarctic Mode Water formation. However, these processes have strong interannual variability; a higher frequency of 2 σ and 3 σ turbulent heat loss events in winter 2015 led to deep mixed layers (>300 m), which were nonexistent in winter 2016.}, issn = {0094-8276}, doi = {10.1029/2017gl076909}, url = {://WOS:000435262000052}, author = {Ogle, S. E. and Tamsitt, V. and Josey, S. A. and Gille, S. T. and Cerovecki, I. and Talley, L. D. and Weller, R. A.} } @article {RN86, title = {Geostatistical Analysis of Mesoscale Spatial Variability and Error in SeaWiFS and MODIS/Aqua Global Ocean Color Data}, journal = {Journal of Geophysical Research: Oceans}, volume = {123}, number = {1}, year = {2018}, pages = {22-39}, type = {Journal Article}, abstract = {Mesoscale (10{\textendash}300 km, weeks to months) physical variability strongly modulates the structure and dynamics of planktonic marine ecosystems via both turbulent advection and environmental impacts upon biological rates. Using structure function analysis (geostatistics), we quantify the mesoscale biological signals within global 13 year SeaWiFS (1998{\textendash}2010) and 8 year MODIS/Aqua (2003{\textendash}2010) chlorophyll a ocean color data (Level-3, 9 km resolution). We present geographical distributions, seasonality, and interannual variability of key geostatistical parameters: unresolved variability or noise, resolved variability, and spatial range. Resolved variability is nearly identical for both instruments, indicating that geostatistical techniques isolate a robust measure of biophysical mesoscale variability largely independent of measurement platform. In contrast, unresolved variability in MODIS/Aqua is substantially lower than in SeaWiFS, especially in oligotrophic waters where previous analysis identified a problem for the SeaWiFS instrument likely due to sensor noise characteristics. Both records exhibit a statistically significant relationship between resolved mesoscale variability and the low-pass filtered chlorophyll field horizontal gradient magnitude, consistent with physical stirring acting on large-scale gradient as an important factor supporting observed mesoscale variability. Comparable horizontal length scales for variability are found from tracer-based scaling arguments and geostatistical decorrelation. Regional variations between these length scales may reflect scale dependence of biological mechanisms that also create variability directly at the mesoscale, for example, enhanced net phytoplankton growth in coastal and frontal upwelling and convective mixing regions. Global estimates of mesoscale biophysical variability provide an improved basis for evaluating higher resolution, coupled ecosystem-ocean general circulation models, and data assimilation.}, issn = {2169-9275}, doi = {10.1002/2017JC013023}, url = {https://doi.org/10.1002/2017JC013023}, author = {Glover, David M. and Doney, Scott C. and Oestreich, William K. and Tullo, Alisdair W.} } @article {RN10, title = {Observation and Modeling of Hydrothermal Response to the 2015 Eruption at Axial Seamount, Northeast Pacific}, journal = {Geochemistry, Geophysics, Geosystems}, number = {ja}, year = {2018}, type = {Journal Article}, abstract = {The 2015 eruption at Axial Seamount, an active volcano at a depth of 1500 m in the Northeast Pacific, marked the first time a seafloor eruption was detected and monitored by an in situ cabled observatory{\textemdash}the Cabled Array, which is part of the Ocean Observatories Initiative. After the onset of the eruption, eight cabled and noncabled instruments on the seafloor recorded unusual, nearly synchronous and spatially uniform temperature increases of 0.6{\textendash}0.7{\textdegree}C across the southern half of the caldera and neighboring areas. These temperature signals were substantially different from those observed after the 2011 and 1998 eruptions at Axial and hence cannot be explained by emplacement of the 2015 lava flows on the seafloor. In this study, we investigate several possible explanations for the 2015 temperature anomalies and use a numerical model to test our preferred hypothesis that the temperature increases were caused by the release of a warm, dense brine that had previously been stored in the crust. If our interpretation is correct, this is the first time that the release of a hydrothermal brine has been observed due to a submarine eruption. This observation would have important implications for the salt balance of hydrothermal systems and the fate of brines stored in the subsurface. The observation of the 2015 temperature anomalies and the modeling presented in this study also demonstrate the importance of contemporaneous water column observations to better understand hydrothermal impacts of submarine eruptions.}, issn = {15252027}, doi = {10.1029/2018gc007607}, url = {https://agupubs.onlinelibrary.wiley.com/doi/abs/10.1029/2018GC007607}, author = {Xu, Guangyu and Chadwick, William W. and Wilcock, William S. D. and Bemis, Karen G. and Delaney, John} } @article {RN28, title = {A regime-dependent retrieval algorithm for near-surface air temperature and specific humidity from multi-microwave sensors}, journal = {Remote Sensing of Environment}, volume = {215}, year = {2018}, pages = {199-216}, type = {Journal Article}, abstract = {Near-surface specific humidity (qa) and air temperature (Ta) over the global ocean are important meteorological variables, but they cannot be retrieved directly from remote sensing. Many efforts have been made to develop algorithms that derive qa and Ta from multisensor microwave and/or infrared observations using in situ measurements as training datasets. However, uncertainty remains large in the resultant qa and Ta retrievals. In this study, 147 moored surface buoys are used to examine how buoy measured qa and Ta are related to satellite microwave brightness temperature (Tb) on the spatial scale from the warm/humid tropics to the cold/dry high latitudes. It is found that the Tb {\textendash} qa and Tb {\textendash} Ta relations are structured along two distinct, near-linear bands, with the primary band in the warm/humid regime and a secondary (weaker) band in the cold/dry regime. The step-like transition (or separation) between the two regimes occurs at 8{\textendash}10 g kg-1 for qa and 14{\textendash}17 {\textdegree}C for Ta. The evidence suggests that one algorithm may not be sufficient to extract qa and Ta from Tb in all regimes. Therefore, a high-latitude enhancement is added to the global algorithm so that the qa and Ta retrievals in the dry/cold regime can be specifically addressed. The new algorithms are applied to 11 microwave sensors, including SSM/I, SSMIS, and AMSU-A, from 1988 to 2016. Based on the 475,717 buoy collocations during the 29-year period, the retrieved qa and Ta have root-mean-square differences of 0.82 g kg-1 and 0.51 {\textdegree}C, respectively. }, keywords = {Microwave passive sensors, Moored surface buoys, Multisensor retrieval, Near-surface air temperature and specific humidity, Retrieval algorithm}, issn = {00344257}, doi = {10.1016/j.rse.2018.06.001}, url = {https://staging-ddpp.dimensions.ai/details/publication/pub.1104605412}, author = {Yu, Lisan and Jin, Xiangze} } @article {RN91, title = {The O2/N2 Ratio and CO2 Airborne Southern Ocean Study}, journal = {Bulletin of the American Meteorological Society}, volume = {99}, number = {2}, year = {2017}, pages = {381-402}, type = {Journal Article}, abstract = {The Southern Ocean plays a critical role in the global climate system by mediating atmosphere{\textendash}ocean partitioning of heat and carbon dioxide. However, Earth system models are demonstrably deficient in the Southern Ocean, leading to large uncertainties in future air{\textendash}sea CO2 flux projections under climate warming and incomplete interpretations of natural variability on interannual to geologic time scales. Here, we describe a recent aircraft observational campaign, the O2/N2 Ratio and CO2 Airborne Southern Ocean (ORCAS) study, which collected measurements over the Southern Ocean during January and February 2016. The primary research objective of the ORCAS campaign was to improve observational constraints on the seasonal exchange of atmospheric carbon dioxide and oxygen with the Southern Ocean. The campaign also included measurements of anthropogenic and marine biogenic reactive gases; high-resolution, hyperspectral ocean color imaging of the ocean surface; and microphysical data relevant for understanding and modeling cloud processes. In each of these components of the ORCAS project, the campaign has significantly expanded the amount of observational data available for this remote region. Ongoing research based on these observations will contribute to advancing our understanding of this climatically important system across a range of topics including carbon cycling, atmospheric chemistry and transport, and cloud physics. This article presents an overview of the scientific and methodological aspects of the ORCAS project and highlights early findings.}, issn = {0003-0007}, doi = {10.1175/BAMS-D-16-0206.1}, url = {https://doi.org/10.1175/BAMS-D-16-0206.1}, author = {Stephens, Britton B. and Long, Matthew C. and Keeling, Ralph F. and Kort, Eric A. and Sweeney, Colm and Apel, Eric C. and Atlas, Elliot L. and Beaton, Stuart and Bent, Jonathan D. and Blake, Nicola J. and Bresch, James F. and Casey, Joanna and Daube, Bruce C. and Diao, Minghui and Diaz, Ernesto and Dierssen, Heidi and Donets, Valeria and Gao, Bo-Cai and Gierach, Michelle and Green, Robert and Haag, Justin and Hayman, Matthew and Hills, Alan J. and Hoecker-Mart{\'\i}nez, Mart{\'\i}n S. and Honomichl, Shawn B. and Hornbrook, Rebecca S. and Jensen, Jorgen B. and Li, Rong-Rong and McCubbin, Ian and McKain, Kathryn and Morgan, Eric J. and Nolte, Scott and Powers, Jordan G. and Rainwater, Bryan and Randolph, Kaylan and Reeves, Mike and Schauffler, Sue M. and Smith, Katherine and Smith, Mackenzie and Stith, Jeff and Stossmeister, Gregory and Toohey, Darin W. and Watt, Andrew S.} }