Bacterial Diversity in Sea Ice from the Southern Ocean and the Sea of Okhotsk

In context of rapid environmental change, the investigation of vulnerable parts of the global climate system is the focus of recent research. The assessment of global interactions between a changing climate and Antarctic sea ice, especially at the rapidly warming Western Antarctic Peninsula (WAP), aims to improve climate and ice sheet modelling for future projections. For this, the reconstruction of past sea ice distribution provides crucial information to enhance the capability of climate models. The goal of this thesis is the evaluation of the novel organic sea ice biomarker IPSO25 (ice proxy for the Southern Ocean with 25 carbon atoms) and its application as a new tool for past sea ice reconstructions analogously to its counterpart IP25 in the Arctic Ocean. This organic biomarker is a source specific organic compound from sea ice algae and associated with Antarctic spring sea ice. Information about the significance and limitations of this sea ice biomarker is still sparse and shall be revealed by using surface and downcore marine sediments. Comparisons to independent data such as biomarkers for open marine conditions, diatom assemblages, satellites data, ice core and marine sediment records improve the precise assessment of IPSO25. The distribution and evaluation of IPSO25 with recent sea ice data is the topic of the first study (Part I). The multiproxy investigation of surface sediment samples from the Drake Passage and the WAP reveals a good agreement of IPSO25 with ecological diatom data and satellite sea ice observations. The implementation of a sea ice index from combined open marine and sea ice biomarkers – PIPSO25 – implies that this tool is promising for paleo sea ice studies. The following two investigations (Part II and III) cover the last 200 a and 17 ka BP, respectively, based on three short and one long sediment records, and highlight the regional significance of IPSO25. Evaluation of the relation to sea salt sodium, methanesulfonic acid, numerical model output and reconstructed atmospheric circulation patterns (El Nino Southern Oscillation, Southern Annular Mode and Southern Westerly Winds) reveals that IPSO25 and PIPSO25 more likely indicate seasonal and dynamic sea ice changes than sea ice quantities. The development of past sea ice during the deglaciation and the Holocene at the WAP shows a significant change in sea ice seasonality in agreement with past investigations. The influence of the El Nino Southern Oscillation, the Southern Annular Mode and the Southern Westerly Winds is evident in sea ice biomarker production pattern due to high variability and the latitudinal position of westerly winds at the WAP. This thesis provides new reference data for paleo sea ice studies and provides a first research approach in further application of IPSO25, PIPSO25 and paleo sea ice investigations in Antarctica and the Southern Ocean.

The changes invoked in the Southern Ocean physics are dynamically linked to Southern Hemisphere westerlies, ocean currents, and Antarctic sea ice distribution. Therefore, it is necessary to understand the response of the Southern Ocean dynamics to the Antarctic sea ice distribution on a basin scale. This modeling study employs a fully coupled Earth system model to investigate the effect of Antarctic Sea ice distribution on the Southern Ocean Overturning circulation during the past twenty thousand years before the present. The simulation shows that the Southern Ocean surface buoyancy flux influences the Southern Ocean overturning circulation. The results indicate that the formation and melting of Antarctic sea ice feedback affect the coverage of surface buoyancy flux over the Southern Ocean. The simulated sea ice boundary (ocean surface area covered with more than a 5% sea ice fraction) almost demarcates the boundary between the upper and lower meridional overturning cells in the Southern Ocean. The Antarctic quasi-permanent sea ice boundary (ocean surface area covered with more than eighty percent sea ice fraction) overlaps with the transition of surface buoyancy flux from positive (surface buoyancy gain) to negative (surface buoyancy loss). Moreover, similar to the Antarctic sea ice coverage, the negative surface buoyancy flux zone has displaced polewards for the past twenty thousand years except for about 14.1 thousand years. Our study highlights that the melting and formation of Antarctic sea ice modulates the Southern Ocean surface buoyancy flux, which affects the Southern Ocean Overturning circulation.

The sea ice frozen on polar ocean forms a new interface between the upper ocean and the lower atmosphere. Sea ice plays an important part in the climate and environment system of Earth through its modifying role in radiative and energy balances, prevent the exchange of heat and moisture between the ocean and atmosphere. The salt reject during processes of sea ice freezing affects the ocean structure and circulation. Sea ice also affects the weather and climate at the South Ocean and Antarctic continent. The area of Antarctic sea ice takes about 58% of all the area of south hemisphere cryosphere, and 3.58% of Earth surface area. The seasonal sea ice area in Antarctica is about 83% of all sea ice area. The area of sea ice in Antarctica decreases to the smallest, about 3×10~6km~2, at February in the end of Austral summer; the area increases to the largest, around 18×10~6km~2,at September in the end of Austral winter, the fluctuant range for one year-living sea ice is about 15×10~6km~2. The seasonal change of sea ice is larger than 500%, one of the greatest seasonal surface changes on Earth. The inter-annual variations of sea ice zones are big. Antarctic sea ice area is one of key regions, which affect the global climate and environment in season and inter-annual. To understand sea ice processes and the interactions between ocean and atmosphere in sea ice area are the main objectives of international Antarctic sea ice and climate programs. Some progresses of research on sea ice and clime, and international programs on Antarctic sea ice are reviewed.

Abstract. An operational synoptic-scale sea ice forecasting system for the Southern Ocean, namely the Southern Ocean Ice Prediction System (SOIPS), has been developed to support ship navigation in the Antarctic sea ice zone. Practical application of the SOIPS forecasts had been implemented for the 38th Chinese National Antarctic Research Expedition for the first time. The SOIPS is configured on an Antarctic regional sea ice–ocean–ice shelf coupled model and an ensemble-based localized error subspace transform Kalman filter data assimilation model. Daily near-real-time satellite sea ice concentration observations are assimilated into the SOIPS to update sea ice concentration and thickness in the 12 ensemble members of the model state. By evaluating the SOIPS performance in forecasting sea ice metrics in a complete melt–freeze cycle from 1 October 2021 to 30 September 2022, this study shows that the SOIPS can provide reliable Antarctic sea ice forecasts. In comparison with non-assimilated EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) data, annual mean root mean square errors in the sea ice concentration forecasts at a lead time of up to 168 h are lower than 0.19, and the integrated ice edge errors in the sea ice forecasts in most freezing months at lead times of 24 and 72 h maintain around 0.5×106 km2 and below 1.0×106 km2, respectively. With respect to the scarce Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) observations, the mean absolute errors in the sea ice thickness forecasts at a lead time of 24 h are lower than 0.3 m, which is in the range of the ICESat-2 uncertainties. Specifically, the SOIPS has the ability to forecast sea ice drift, in both magnitude and direction. The derived sea ice convergence rate forecasts have great potential for supporting ship navigation on a fine local scale. The comparison between the persistence forecasts and the SOIPS forecasts with and without data assimilation further shows that both model physics and the data assimilation scheme play important roles in producing reliable sea ice forecasts in the Southern Ocean.

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 238:1-13 (2002) - doi:10.3354/meps238001 Particulate organic matter in Antarctic summer sea ice: concentration and stable isotopic composition H. Kennedy1,*, D. N. Thomas1, G. Kattner2, C. Haas2, G. S. Dieckmann2 1School of Ocean Sciences, University of Wales, Bangor, Menai Bridge, Anglesey LL59 5EY, Wales, UK 2Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27515 Bremerhaven, Germany *E-mail: h.a.kennedy@bangor.ac.uk ABSTRACT: The chemical and isotopic data from sea ice collected over a wide area of the Weddell Sea, Antarctica, during the austral summer/early autumn illustrate the range of environmental conditions under which ice algae grow. A range of ice types and features were sampled including intact and layered ice floes and surface ponds. Sea ice communities were found in all these environments but the highest biomasses were found either at the base of ice floes, or in the interior of layered floes with quasi-continuous horizontal gaps at or shortly below the water level. In the layered floes, particulate organic carbon (POC) measured in the ice layer immediately overlying the gap water (280 to 6014 µmol dm-3) was in excess of what would be predicted if algal growth had occurred in a closed environment. The chemical composition of the gap water was strongly affected by biological activity in the overlying ice, which acts as a physical support for the algae retained within its matrix. The lowest range of POC (27 to 739 µmol dm-3) conformed to predictions of algal growth in a closed system and samples were collected from the interior of ice floes where there was essentially no potential for nutrient exchange. The surface ponds displayed nitrate (NO3-) exhaustion and total dissolved inorganic carbon (ΣCO2) reductions consistent with nutrient limited algal growth. The stable carbon isotopic composition of the particulate organic matter (POM) across all habitat types sampled (δ13CPOC -10.0 to -27.3‰) displayed a wide range but was much less variable than the range of POC concentrations might have implied. The assumption that the highest biomass of algae in sea ice will result in the most positive δ13CPOC values cannot be generally applied. The isotopic composition of dissolved inorganic carbon (δ13CΣCO2) in gap waters and surface ponds varied from 0.15 to 3.0‰ and was shown to be commensurate with the changes predicted from NO3- deficits caused by algal growth. KEY WORDS: POM · Antarctic sea ice · Ice macroalgae · Carbon isotopic composition Full text in pdf format NextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 238. Online publication date: August 08, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

Comparison of Arctic and Antarctic sea ice spatial–temporal changes during 1979–2018

In 2016, Antarctic sea ice experienced a regime shift when a persisting decreasing trend emerged from a relatively stable annual cycle. Drivers of the sea ice regime shift and future projections of Southern Ocean sea ice remain unresolved. One possible contributing phenomena are atmospheric rivers (ARs), which are long, narrow, and transient features responsible for the majority of global poleward water vapor transport. Though infrequent over Antarctica, ARs wield a substantial influence on the Antarctic ice mass balance. Previous studies highlight their significance, attributing 35% of the interannual precipitation variability over the Antarctic Ice Sheet (AIS) to ARs. The interaction between ARs and Antarctic sea ice has not been as clearly defined. Our ongoing work uses ERA5 reanalysis data, results from an AR tracking algorithm, and passive microwave sea ice concentration data from 1980 to 2023 to examine the relationship between ARs and Antarctic sea ice, especially in the context of the changing sea ice state. In this study, we explore the relationship between AR activity and sea ice area at a region and seasonal scale, then analyse the contribution of ARs to precipitation over sea ice and how that contribution has changed through the 40-year study period. On average, ARs can be attributed with 11% of total precipitation, 11% of snowfall, and 13% of rain over Antarctic sea ice. While the AR contribution to sea ice snowfall is fairly consistent through the year, the predominant AR contribution to rain rotates around the Southern Ocean sequentially by season. The strongest signal of AR precipitation over sea ice is in the Weddell Sea winter, when ARs constitute 25% of winter rain. The trends of these contributions vary by season and by region. For example, while AR precipitation on sea ice has an increasing trend across all types of precipitation in each season in the Weddell Sea, the opposite is true for the Ross Sea. These findings underscore the importance of the AR interaction with Antarctic sea ice, particularly in the context of seasonal and regional variability and change. This work will improve our understanding of the spatiotemporal variability and trends of ARs as precipitation mechanisms, which is vital for understanding and predicting sea ice mass balance in a changing climate.

This study investigates the response of the Southern Ocean sea surface temperature (SST) and Antarctic sea ice to stratospheric ozone recovery, focusing on the time scale and seasonality of the response. The response is quantified by contrasting two twenty-first-century ensemble simulations conducted with the Goddard Earth Observing System Chemistry–Climate Model: one with decreasing ozone-depleting substances (ODSs) and the other with fixed 2005 levels of ODSs. In our simulations, the response to ozone recovery has large seasonal variations, but it does not show a two-time-scale behavior. Ozone recovery causes Southern Ocean SST warming in austral summer and cooling in other seasons. Ozone recovery mitigates Antarctic sea ice decrease in the twenty-first century in austral spring, fall, and winter. However, the summer Antarctic sea ice extent is not affected by ozone recovery despite strong surface warming, because the warming occurs north of the sea ice edge. The absence of summer sea ice response likely results from the model bias of underestimating summer sea ice climatology. The summer surface warming response is associated with cooling directly below the mixed layer. Temperature tendency budget analysis shows that reduced vertical mixing plays a critical role in driving this vertical dipole temperature response. We also find that the impact of the vertical temperature advection on SST depends not only on changes in upwelling but also on changes in vertical temperature gradient. Significance Statement We study the climate impact of the projected stratospheric ozone recovery in the twenty-first century on Southern Ocean sea surface temperature and Antarctic sea ice using coupled atmosphere–ocean–chemistry model simulations. The model results show that ozone recovery causes weakening of surface winds over the Southern Ocean, which leads to warming of the Southern Ocean surface in summer and cooling in other seasons. Ozone recovery also reduces Antarctic sea ice loss in the twenty-first century. We quantify the relative importance of meridional and vertical advection and vertical mixing in determining the upper Southern Ocean temperature response to stratospheric ozone recovery. These results improve our understanding of how changes in surface winds affect the Southern Ocean temperature, circulation, and Antarctic sea ice.

The Southern Ocean (SO) played a fundamental role in the deglacial climate system by exchanging carbon-rich deep ocean water with the surface. The contribution of the SO’s physical mechanisms toward improving our understanding of SO upwelling’s dynamical changes is developing. Here, we investigated the simulated transient SO atmosphere, ocean, and sea ice evolution during the last deglaciation in a fully coupled Earth system model. Our results showed that decreases in SO upwelling followed the weakening of the Southern Hemisphere surface westerlies, wind stress forcing, and Antarctic sea ice coverage from the Last Glacial Maximum to the Heinrich Stadial 1 and the Younger Dryas. Our results support the idea that the SO upwelling is primarily driven by wind stress forcing. However, during the onset of the Holocene, SO upwelling increased while the strength of the wind stress decreased. The Antarctic sea ice change controlled the salt and freshwater fluxes, ocean density, and buoyancy flux, thereby influencing the SO’s dynamics. Our study highlighted the dynamic linkage of the Southern Hemisphere westerlies, ocean, and sea ice in the SO’s latitudes. Furthermore, it emphasized that zonal wind stress forcing and buoyancy forcing control by sea ice together regulate the change in the SO upwelling.

Synoptic mode of Antarctic summer sea ice superimposed on interannual and decadal variability

The study analyzes the sensitivity and memory of the Southern Hemisphere coupled climate system to increased Antarctic sea ice (ASI), taking into account the persistence of the sea ice maxima in the current climate. The mechanisms involved in restoring the climate balance under two sets of experiments, which differ in regard to their sea ice models, are discussed. The experiments are perturbed with extremes of ASI and integrated for 10 yr in a large 30-member ensemble. The results show that an ASI maximum is able to persist for ~4 yr in the current climate, followed by a negative sea ice phase. The sea ice insulating effect during the positive phase reduces heat fluxes south of 60°S, while at the same time these are intensified at the sea ice edge. The increased air stability over the sea ice field strengthens the polar cell while the baroclinicity increases at midlatitudes. The mean sea level pressure is reduced (increased) over high latitudes (midlatitudes), typical of the southern annular mode (SAM) positive phase. The Southern Ocean (SO) becomes colder and fresher as the sea ice melts mainly through sea ice lateral melting, the consequence of which is an increase in the ocean stability by buoyancy and mixing changes. The climate sensitivity is triggered by the sea ice insulating process and the resulting freshwater pulse (fast response), while the climate equilibrium is restored by the heat stored in the SO subsurface layers (long response). It is concluded that the time needed for the ASI anomaly to be dissipated and/or melted is shortened by the sea ice dynamical processes.

The sea ice concentration dataset (covering the period 1992-2008) used in this study is a new dataset based on the Sea Ice Climate Change Initiative (SICCI) algorithm. We investigate whether the SICCI dataset is on a par with other datasets for studying sea ice cover changes in the Southern Ocean. We then examine spatiotemporal variations in sea ice derived from the SICCI dataset over the Southern Ocean, and analyse relationships of sea ice with sea surface temperature (SST). The results indicate that there is no significant difference between the SICCI dataset and the NASA Team dataset, and therefore the former can also be used for studying sea ice changes. Both sea ice extent (SIE) and sea ice area (SIA) derived from the SICCI dataset over the Southern Ocean increased slightly from 1992 to 2008, at rates of (17.75 ± 11.50) × 10^3 and (17.37 ± 9.51) × 10^3 km^2 yr^(–1), respectively. Antarctic sea ice has significant seasonal variations; all seasonally averaged SIE and SIA show an increase, with spring showing the largest positive changing rate. The Weddell Sea, Ross Sea, and Indian Ocean have positive yearly changing rates in SIE and SIA, while the Bellingshausen/Amundsen seas and western Pacific Ocean have negative yearly changing rates. However, overall sea ice over the Southern Ocean has a slight positive trend, which is the same as the sea ice change pattern derived from the NASA Team dataset. This indicates that the contributions to the change in sea ice over the whole Southern Ocean due to the Weddell Sea, Ross Sea, and Indian Ocean dominate over those by the Bellingshausen/Amundsen seas and western Pacific Ocean. Further analysis shows that both SIE and SIA are negatively correlated with SST in the Southern Ocean or each of the 5 longitudinal sectors, and sea ice is more sensitive to SST in spring and autumn.

Abstract. Iron is a key nutrient for phytoplankton growth in the surface ocean. At high latitudes, the iron cycle is closely related to the dynamics of sea ice. In recent decades, Arctic sea ice cover has been declining rapidly and Antarctic sea ice has exhibited large regional trends. A significant reduction of sea ice in both hemispheres is projected in future climate scenarios. In order to adequately study the effect of sea ice on the polar iron cycle, sea ice bearing iron was incorporated in the Community Earth System Model (CESM). Sea ice acts as a reservoir for iron during winter and releases the trace metal to the surface ocean in spring and summer. Simulated iron concentrations in sea ice generally agree with observations in regions where iron concentrations are relatively low. The maximum iron concentrations simulated in Arctic and Antarctic sea ice are much lower than observed, which is likely due to underestimation of iron inputs to sea ice or missing mechanisms. The largest iron source to sea ice is suspended sediments, contributing fluxes of iron of 2.2 × 108 mol Fe month−1 in the Arctic and 4.1 × 106 mol Fe month−1 in the Southern Ocean during summer. As a result of the iron flux from ice, iron concentrations increase significantly in the Arctic. Iron released from melting ice increases phytoplankton production in spring and summer and shifts phytoplankton community composition in the Southern Ocean. Results for the period of 1998 to 2007 indicate that a reduction of sea ice in the Southern Ocean will have a negative influence on phytoplankton production. Iron transport by sea ice appears to be an important process bringing iron to the central Arctic. The impact of ice to ocean iron fluxes on marine ecosystems is negligible in the current Arctic Ocean, as iron is not typically the growth-limiting nutrient. However, it may become a more important factor in the future, particularly in the central Arctic, as iron concentrations will decrease with declining sea ice cover and transport.

We report first direct measurements of the partial pressure of CO2 (pCO2) within Antarctic pack sea ice brines and related CO2 fluxes across the air‐ice interface. From late winter to summer, brines encased in the ice change from a CO2 large oversaturation, relative to the atmosphere, to a marked undersaturation while the underlying oceanic waters remains slightly oversaturated. The decrease from winter to summer of pCO2 in the brines is driven by dilution with melting ice, dissolution of carbonate crystals, and net primary production. As the ice warms, its permeability increases, allowing CO2 transfer at the air‐sea ice interface. The sea ice changes from a transient source to a sink for atmospheric CO2. We upscale these observations to the whole Antarctic sea ice cover using the NEMO‐LIM3 large‐scale sea ice‐ocean and provide first estimates of spring and summer CO2 uptake from the atmosphere by Antarctic sea ice. Over the spring‐summer period, the Antarctic sea ice cover is a net sink of atmospheric CO2 of 0.029 Pg C, about 58% of the estimated annual uptake from the Southern Ocean. Sea ice then contributes significantly to the sink of CO2 of the Southern Ocean.

Roles of wind stress and thermodynamic forcing in recent trends in Antarctic sea ice and Southern Ocean SST: An ocean-sea ice model study