Southern Ocean Research Articles

Deciphering the Hearts: Geometric Morphometrics Reveals Shape Variation in Abatus Sea Urchins across Subantarctic and Antarctic Seas.

Abatus is a genus of irregular brooding sea urchins to the Southern Ocean. Among the 11 described species, three shared morphological traits and present an infaunal lifestyle in the infralittoral from the Subantarctic province; A. cavernosus in Patagonia, A. cordatus in Kerguelen, and A. agassizii in Tierra del Fuego and South Shetlands. The systematic of Abatus, based on morphological characters and incomplete phylogenies, is complex and largely unresolved. This study evaluates the shape variation among these species using geometric morphometrics analysis (GM). For this, 72 individuals from four locations; South Shetlands, Kerguelen, Patagonia, and Falklands/Malvinas were photographed, and 37 landmarks were digitized. To evaluate the shape differences among species, a principal component analysis and a Procrustes ANOVA were performed. Our results showed a marked difference between the Falklands/Malvinas and the other localities, characterized by a narrower and more elongated shape and a significant influence of location in shape but not sex. Additionally, the effect of allometry was evaluated using a permutation test and a regression between shape and size, showing significant shape changes during growth in all groups. The possibility that the Falklands/Malvinas group shows phenotypic plasticity or represents a distinct evolutionary unit is discussed. Finally, GM proved to be a powerful tool to differentiate these species, highlighting its utility in systematic studies.

Scaling up ocean conservation through recognition of key biodiversity areas in the Southern Ocean from multispecies tracking data.

Biodiversity is critical for maintaining ecosystem function but is threatened by increasing anthropogenic pressures. In the Southern Ocean, a highly biologically productive region containing many endemic species, proactive management is urgently needed to mitigate increasing pressures from fishing, climate change, and tourism. Site-based conservation is one important tool for managing the negative impacts of human activities on ecosystems. The Key Biodiversity Area (KBA) Standard is a standardized framework used to define sites vital for the persistence of global biodiversity based on criteria and quantitative thresholds. We used tracking data from 14 species of Antarctic and subantarctic seabirds and pinnipeds from the publicly available Retrospective Analysis of Antarctic Tracking Data (RAATD) data set to define KBAs for a diverse suite of marine predators. We used track2kba, an R package that supports identification of KBAs from telemetry data through identification of highly used habitat areas and estimates of local abundance within sites. We compared abundance estimates at each site with thresholds for KBA criteria A1, B1, and D1 (related to globally threatened species, individual geographically restricted species, and demographic aggregations, respectively). We identified 30 potential KBAs for 13 species distributed throughout the Southern Ocean that were vital for each individual species, population, and life-history stage for which they were determined. These areas were identified as highly used by these populations based on observational data and complement the ongoing habitat modeling and bioregionalization work that has been used to prioritize conservation areas in this region. Although further work is needed to identify potential KBAs based on additional current and future data sets, we highlight the benefits of utilizing KBAs as part of a holistic approach to marine conservation, given their significant value as a global conservation tool.

Influence of migration range and foraging ecology on mercury accumulation in Southern Ocean penguins

In order to evaluate mercury (Hg) accumulation patterns in Southern Ocean penguins, we measured Hg concentrations and carbon (δ13C) and nitrogen (δ15N) stable isotope ratios in body feathers of adult Adélie (Pygoscelis adeliae), gentoo (Pygoscelis papua), and chinstrap (Pygoscelis antarctica) penguins living near Anvers Island, West Antarctic Peninsula (WAP) collected in the 2010/2011 austral summer. With these and data from Pygoscelis and other penguin genera (Eudyptes and Aptenodytes) throughout the Southern Ocean, we modelled Hg variation using δ13C and δ15N values. Mean concentrations of Hg in feathers of Adélie (0.09 ± 0.05 μg g−1) and gentoo (0.16 ± 0.08 μg g−1) penguins from Anvers Island were among the lowest ever reported for the Southern Ocean. However, Hg concentrations in chinstrap penguins (0.80 ± 0.20 μg g−1), which undertake relatively broad longitudinal winter migrations north of expanding sea ice, were significantly higher (P < 0.001) than those in gentoo or Adélie penguins. δ13C and δ15N values for feathers from all three Anvers Island populations were also the lowest among those previously reported for Southern Ocean penguins foraging within Antarctic and subantarctic waters. These observations, along with size distributions of WAP krill, suggest foraging during non-breeding seasons as a primary contributor to higher Hg accumulation in chinstraps relative to other sympatric Pygoscelis along the WAP. δ13C values for all Southern Ocean penguin populations, alone best explained feather Hg concentrations among possible generalized linear models (GLMs) for populations grouped by either breeding site (AICc = 36.9, wi = 0.0590) or Antarctic Frontal Zone (AICc = 36.9, wi = 0.0537). Although Hg feather concentrations can vary locally by species, there was an insignificant species-level effect (wi < 0.001) across the full latitudinal range examined. Therefore, feeding ecology at breeding locations, as tracked by δ13C, control Hg accumulation in penguin populations across the Southern Ocean.

Interplays between the BBNJ Agreement and the Antarctic Treaty System on the Southern Ocean bioprospecting

The Southern Ocean is witnessing an increasing prevalence of bioprospecting. Within the context of the Antarctic Treaty System (ATS), bioprospecting issues have been discussed over years, while a consensus on the specialized regulation of related activities remains elusive. On June 20, 2023, the BBNJ Agreement was formally adopted, featuring specific provisions addressing marine genetic resources (MGRs). This paper explores the interplay between the BBNJ Agreement and the ATS to promote the management of bioprospecting in Southern Ocean. It begins by discussing the relationship between the ATS and the BBNJ Agreement under the theory of institutional interplay, then delves into the evolutionary of the Southern Ocean bioprospecting discussions under the ATS, and examines the regulatory stipulations pertaining to MGRs in the BBNJ Agreement. It concludes that although there is a competitive relationship between the two on bioprospecting issues, this does not preclude the possibility of beneficial interplays. The ATS can gain insights from the access and benefit-sharing mechanisms for MGRs and the information exchange regimes of the BBNJ Agreement, thereby expediting the establishment of a legal framework governing Southern Ocean bioprospecting within the ATS.

Hydro-Rugging as Reparative Caring Encounter: Re-Membering Southern Oceanic Hauntologies

ABSTRACT Expanding beach clean-ups to more than just removing plastic from the shoreline, citizens are invited to dwell with the ecological crisis and its intersectional entanglements of historical injustices related to the ocean, through a tactile mending practice using collected rubbish. Public story-doing (Rodricks, 2024) [Towards a (strategic) sensibility of unbelonging: Full participation revisited. International Journal of Qualitative Studies in Education, 1–15] is initiated by generative dialogue enabled through the material call of the collected plastic which is re-membered and mended into the Mother Hydro-rug. This making-with thinking/theorising (Haraway, 2016 [Staying with the trouble: Making kin in the Chthulucene. Duke University Press]; Manning, 2016 [The minor gesture. Duke University Press]) involves re-membering erased narratives that entangle people with the ocean. Hydro-rugging fosters reparative care practices within vulnerable communities through convivial organised events that bring together people, particularly Black and Brown bodies, together to share their memories of and with the ocean. Hydro-rugging embodies the importance of active listening and acknowledging emotions (Ahmed, 2004) [The cultural politics of emotion. University Press], engaging in a call and response with the very fabric of beach surroundings, be it the plastic or other more-than-human elements.

Southern Ocean heat buffer constrained by present-day ENSO teleconnection

The heat storage capacity of Southern Ocean (SO) buffers future atmospheric warming but differs vastly across climate models. Reducing its projection uncertainty is vital for understanding and evaluating future global sustainability. Using Coupled Model Intercomparison Project Phase 6, we show that the present-day SO high-latitude easterly wind anomalies induced by El Niño is an effective constraint for the projected increase in SO heat content. Models simulating weaker El Niño-induced easterlies generate more equatorward atmospheric teleconnection in the present day. Under global warming, these models have greater capacity in the poleward shift of atmospheric circulation, thus generate stronger future increase in El Niño-induced high-latitude easterlies, slowing the SO heat storage by weakening the northward Ekman transport that underpins the dynamical process for SO heat storage. However, most models overestimate the present-day El Niño-induced easterlies, implying that alleviating this bias would reduce future SO heat storage, thus exacerbating atmospheric warming.

Stable carbon isotopes in scallop shells: A proxy of Antarctic sea-ice persistence

Sea ice is fundamental to global climate and its multiannual persistence or seasonal absence shapes Antarctic marine ecosystems. With sea ice in rapid decline in the Southern Ocean, it is imperative to understand its variability prior to satellite data. The Antarctic scallop Adamussium colbecki has a broad geographic distribution and long fossil history in the Southern Ocean, and its shells could be ideal bioarchives for sea ice with the potential to resolve subannual sea-ice dynamics over multiple years or decades. Here, we evaluate stable isotopes of carbon in A. colbecki shells from two sites on western McMurdo Sound. Each site maintains stable, frigid seawater temperatures, but they differ in sea-ice duration. Explorers Cove has semi-permanent multiannual sea ice, whereas Bay of Sails has annual sea ice that breaks out every year. Our results indicate that seasonal variation in δ13Cshell values may proxy sea-ice persistence. Scallops living under annual sea ice — adults from Bay of Sails and juveniles collected during a fortuitous recent sea ice breakout at Explorers Cove — had higher δ13Cshell values during summer growth than winter growth. Scallops living under multi-annual sea ice had no difference in δ13Cshell values between winter and summer growth. We posit that phytoplankton blooms leverage the seasonal δ13C values of the dissolved inorganic carbon under ice-free conditions, which is in turn recorded in δ13Cshell values and that A. colbecki shells could be used to understand past variability in sea-ice persistence in coastal Antarctica.

Osteology provides insight into the biology of the enigmatic Antarctic notothenioid fish Gvozdarus svetovidovi

Gvozdarus svetovidovi (Nototheniidae) is the rarest notothenioid fish, represented by only two specimens collected in 1970 and 1988. As it is little known, we present aspects of the cranial osteology of this species and use this, and other features of its morphology, to infer fundamental aspects of its biology. As in other pelagic nototheniids, G. svetovidovi has an elongated neurocranium and jaws but it does not have a paedomorphic skeleton. Although not unique to G. svetovidovi, the bones of the skull have some well-developed ridges for support and possibly for containment of subcutaneous fat. The skeleton is most similar to that of Dissostichus. G. svetovidovi has a high fat content, primarily within the trunk musculature and in a layer over the skull. It is probably neutrally buoyant in mesopelagic waters, where it has been captured at 295–550 m depth north of the Antarctic Slope Front (approximately the shelf break) and south of the southern boundary of the Antarctic Circumpolar Current. It likely relies on vision and mechanosensation to detect its prey, including bioluminescent, energy-dense myctophids and krill in this resource-rich area of the Southern Ocean. Strays near shelf waters feed on Pleuragramma antarcticum. G. svetovidovi is unlike all other notothenioids in fundamental aspects of its biology including its habitat, diet and distribution. Although it may be on the path to extinction, if our postulated life history of G. svetovidovi is accurate, it expands the current perception of the bounds of the notothenioid radiation into a locality in the Southern Ocean not previously known to be occupied by this group.

Spatially Resolved Temperature Response Functions to CO2 Emissions

AbstractCarbon dioxide (CO2) emissions affect local temperature; quantifying that local response is important for learning about the earth system, the impacts of mitigation, and adaptation needs. We assume the climate system can be represented as a time‐dependent linear system, diagnosing Green's Functions for the spatial temperature response to CO2 emissions based on CMIP6 earth system models. This allows us to emulate the linear component of the temperature response to CO2. This approach is sufficient to capture the spatial temperature response of CMIP6 experiments within one standard deviation of the multimodel spread across most regions, though accuracy is lower in the Southern Ocean and the Arctic. Our approach reveals where nonlinear feedbacks are important in current CMIP6 models, and where the local system response is well represented by a time‐dependent linear differential operator. It incorporates emissions path dependency and may be useful for evaluating large ensembles of emission scenarios.

Assessing the Tropospheric Temperature and Humidity Simulations in CMIP3/5/6 Models Using the AIRS Obs4MIPs V2.1 Data

AbstractIn this study, the Atmospheric Infrared Sounder (AIRS) Observations for Model Intercomparison Projects (Obs4MIPs) V2.1 tropospheric air temperature, specific humidity, and relative humidity data are utilized to evaluate the global tropospheric temperature and humidity simulations in the fully coupled global climate models from the Coupled Model Intercomparison Project phases 3, 5, and 6 (CMIP3, CMIP5, and CMIP6), and possible simulation improvement in CMIP6 models in comparison to CMIP3 and CMIP5 models. Our analyses indicate that all three phases of CMIP models share similar tropospheric air temperature, specific humidity, and relative humidity biases in their multi‐model ensemble means relative to AIRS. Cold biases up to 4 K and positive relative humidity biases up to 20% are found in the free troposphere almost globally with maxima over the mid‐latitude storm tracks. Warm biases up to 2 K are seen over the Southern Ocean in the lower troposphere. Positive specific and relative humidity biases exist over the off‐equatorial oceans while negative specific and relative humidity biases are seen near the equator in the tropical free troposphere, which are related to the double‐intertropical convergence zone bias in the models. Both the air temperature and specific humidity biases are important to the relative humidity biases except in the tropical free troposphere where the specific humidity biases dominate. The tropospheric air temperature, specific humidity, and relative humidity biases are reduced from CMIP3 to CMIP5 and to CMIP6 at almost all pressure levels except at 300 hPa for specific humidity and in the boundary layer for relative humidity.

IWC Database-Estimation and Software System

The International Whaling Commission’s (IWC) Database‐Estimation and Software System (DESS) was designed to standardise IWC line‐transect survey data storage and streamline abundance estimation, including abundance estimation by small management area to inform decision making. Not only was DESS designed to accommodate all International Decade of Cetacean Research (IDCR) and Southern Ocean Whale and Ecosystem Research (SOWER) surveys, but also national surveys, such as the Japanese surveys in the Antarctic and North Pacific, and multi‐national surveys conducted in the North Atlantic. The standard software for estimating abundance was program Distance, which could estimate abundance in designed survey blocks, however, management procedures required estimation not just in survey blocks but also in smaller regions that could be defined by the user. This added a spatial component to data selection which led to the inclusion of a geographical information system (GIS). This paper describes the data stored in DESS and the features available for data retrieval and analysis.

Distributions of nutrients, trace metals, phytoplankton composition, and elemental consumption in the Ross and Amundsen Seas

The Southern Ocean (SO) not only functions as an important carbon sink but also serves as a crucial source of intermediate and deep waters to lower latitudes. The Ross Sea and Amundsen Sea in the West Antarctic are highly productive regions of the Southern Ocean, critically vulnerable to climate change. Hence, comprehending the source-sink patterns of nutrients, particularly trace metals, in these regions is of paramount significance for understanding their ecological effect and the effect on elemental distribution in global ocean. Here, we reported the surface and vertical distributions of phytoplankton composition, Chlorophyll-a (Chl-a), particulate organic carbon (POC), macronutrients, and trace metals (TMs) in the Ross and Amundsen Seas. Deplete dissolved iron concentrations were observed in surface waters averaging 0.17 ± 0.09 nM. High POC and Chl-a were observed that corresponded to elevated Fe in shallow subsurface water (100–300 m), while low POC and Chl-a were found to associate with depleted iron (∼0.1 nM) throughout the upper water column down to 300 m. Sea-ice melting and islands were found to be possible external TMs sources in the Amundsen Sea offshore. Phytoplankton act as a sink for trace metals and regulate the elemental concentration and composition of water bodies, while also being influenced by environmental conditions such as temperature, salinity, and the mixing layer depth. Elemental consumptions in surface water were associated with diatom abundance in both Ross and Amundsen Seas. Based on elemental drawndown ratios in the surface mixed layer, the stoichiometries of the two major phytoplankton functional groups, diatoms and haptophytes, were estimated. Our observations offered insights into the relationships among iron supply, nutrients distribution patterns, and phytoplankton composition in the Southern Ocean.

Pathways and timescales of Southern Ocean hydrothermal iron and manganese transport

Scarcity of iron and manganese limits the efficiency of the biological carbon pump over large areas of the Southern Ocean. The importance of hydrothermal vents as a source of these micronutrients to the euphotic zone of the Southern Ocean is debated. Here we present full depth profiles of dissolved and total dissolvable trace metals in the remote eastern Pacific sector of the Southern Ocean (55–60° S, 89.1° W), providing evidence of enrichment of iron and manganese at depths of 2000–4000 m. These enhanced micronutrient concentrations were co-located with 3He enrichment, an indicator of hydrothermal fluid originating from ocean ridges. Modelled water trajectories revealed the understudied South East Pacific Rise and the Pacific Antarctic Ridge as likely source regions. Additionally, the trajectories demonstrate pathways for these Southern Ocean hydrothermal ridge-derived trace metals to reach the Southern Ocean surface mixed layer within two decades, potentially supporting a regular supply of micronutrients to fuel Southern Ocean primary production.

The latest shallow-sea isocrinids from the Miocene of Paratethys and implications to the Mesozoic marine revolution

The predation-driven Mesozoic marine revolution (MMR) is believed to have induced a dramatic change in the bathymetric distribution of many shallow marine invertebrates since the late Mesozoic. For instance, stalked crinoids – isocrinids (Isocrinida) have undergone a striking decline in shallow-sea environments and today they are restricted to deep-sea settings (below 100 m depth). However, the timing and synchronicity of this shift are a matter of debate. A delayed onset of MMR and/or shifts to a retrograde, low-predation community structure during the Paleogene in the Southern Ocean were invoked. In particular, recent data from the Southern Hemisphere suggest that the environmental restriction of isocrinids to the deep-sea settings may have occurred at the end of the Eocene around Antarctica and Australia, and later in the early Miocene in New Zealand. Here, we report the anomalous occurrence of the isocrinids in shallow nearshore marine facies from the middle Miocene of Poland (Northern Hemisphere, Central Paratethys). Thus, globally, this is the youngest record of shallow-sea stalked crinoids. This finding suggests that some relict stalked crinoids may have been able to live in the shallow-water environments by the middle Miocene, and further confirms that the depth restriction of isocrinids to offshore environments was not synchronous on a global scale.

Climate change is associated with higher phytoplankton biomass and longer blooms in the West Antarctic Peninsula

The Antarctic Peninsula (West Antarctica) marine ecosystem has undergone substantial changes due to climate-induced shifts in atmospheric and oceanic temperatures since the 1950s. Using 25 years of satellite data (1998-2022), this study presents evidence that phytoplankton biomass and bloom phenology in the West Antarctic Peninsula are significantly changing as a response to anthropogenic climate change. Enhanced phytoplankton biomass was observed along the West Antarctic Peninsula, particularly in the early austral autumn, resulting in longer blooms. Long-term sea ice decline was identified as the main driver enabling phytoplankton growth in early spring and autumn, in parallel with a recent intensification of the Southern Annular Mode (2010-ongoing), which was observed to influence regional variability. Our findings contribute to the understanding of the complex interplay between environmental changes and phytoplankton responses in this climatically key region of the Southern Ocean and raise important questions regarding the far-reaching consequences that these ecological changes may have on global carbon sequestration and Antarctic food webs in the future.

Mid-Pleistocene climate transition triggered by Antarctic Ice Sheet growth.

Despite extensive investigation, the nature and causes of the Mid-Pleistocene Transition remain enigmatic. In this work, we assess its linkage to asynchronous development of bipolar ice sheets by synthesizing Pleistocene mid- to high-latitude proxy records linked to hemispheric ice sheet evolution. Our results indicate substantial growth of the Antarctic Ice Sheets (AISs) at 2.0 to 1.25 million years ago, preceding the rapid expansion of Northern Hemisphere Ice Sheets after ~1.25 million years ago. Proxy-model comparisons suggest that AIS and associated Southern Ocean sea ice expansion can induce northern high-latitude cooling and enhanced moisture transport to the Northern Hemisphere, thus triggering the Mid-Pleistocene Transition. The dynamic processes involved are crucial for assessing modern global warming that is already inducing asynchronous bipolar melting of ice sheets.

From spatial prioritization to conservation management in the Southern Ocean using the marine IBAs approach

Implementing effective conservation action requires spatial prioritization exercises to be functionally integrated with a process for developing an implementation strategy. There is great potential for animal tracking data to inform marine management in the Southern Ocean. Using information on penguin distribution, a set of marine Important Bird Areas (mIBAs) has recently been identified around Antarctica. Large-scale spatial analyses like this are key to guide resources and the attention of decision-makers towards areas of significant value. Yet, protecting marine resources requires translating prioritization exercises into legally-binding conservation measures. Here we use one of the largest gentoo colonies in Antarctica as a case study to explore pathways for the utilization of the mIBAs approach in the design and implementation of conservation measures in the Southern Ocean. For scientists and organizations willing to have a policy impact, there are two main routes to contribute to Antarctic Treaty System (ATS) decision-making: through Parties' National Delegations, or through Experts and Observers. We provide three main recommendations for incorporating the results of spatial prioritization analyses into the agenda of ATS governance bodies using the mIBAs approach: 1. Differentiate the potential contribution of mIBAs to spatial prioritization from the potential contribution to conservation planning, two different stages in the conservation process; 2. Use methods, criteria and data for delineating boundaries of potential conservation areas according to the stage of the conservation process that the outputs are expected to contribute to; 3. Understand how Antarctic mIBAs might fit into the ATS conservation measures framework and ongoing deliberations.

Differential association of key bacterial groups with diatoms and Phaeocystis spp. during spring blooms in the Southern Ocean.

Interactions between phytoplankton and heterotrophic bacteria significantly influence the cycling of organic carbon in the ocean, with many of these interactions occurring at the micrometer scale. We explored potential associations between specific phytoplankton and bacteria in two size fractions, 0.8-3 µm and larger than 3 µm, at three naturally iron-fertilized stations and one high nutrient low chlorophyll station in the Southern Ocean. The composition of phytoplankton and bacterial communities was determined by sequencing the rbcL gene and 16S rRNA gene from DNA and RNA extracts, which represent presence and potential activity, respectively. Diatoms, particularly Thalassiosira, contributed significantly to the DNA sequences in the larger size fractions, while haptophytes were dominant in the smaller size fraction. Correlation analysis between the most abundant phytoplankton and bacterial operational taxonomic units revealed strong correlations between Phaeocystis and picoeukaryotes with SAR11, SAR116, Magnetospira, and Planktomarina. In contrast, most Thalassiosira operational taxonomic units showed the highest correlations with Polaribacter, Sulfitobacteria, Erythrobacter, and Sphingobium, while Fragilariopsis, Haslea, and Thalassionema were correlated with OM60, Fluviicola, and Ulvibacter. Our in-situ observations suggest distinct associations between phytoplankton and bacterial taxa, which could play crucial roles in nutrient cycling in the Southern Ocean.

Low-latitude mesopelagic nutrient recycling controls productivity and export.

Low-latitude (LL) oceans account for up to half of global net primary production and export1-5. It has been argued that the Southern Ocean dominates LL primary production and export6, with implications for the response of global primary production and export to climate change7. Here we applied observational analyses and sensitivity studies to an individual model to show, instead, that 72% of LL primary production and 55% of export is controlled by local mesopelagic macronutrient cycling. A total of 34% of the LL export is sustained by preformed macronutrients supplied from the Southern Ocean via a deeper overturning cell, with a shallow preformed northward supply, crossing 30° S through subpolar and thermocline water masses, sustaining only 7% of the LL export. Analyses of five Coupled Model Intercomparison Project Phase 6 (CMIP6) models, run under both high-emissions low-mitigation (shared socioeconomic pathway (SSP5-8.5)) and low-emissions high-mitigation (SSP1-2.6) climate scenarios for 1850-2300, revealed significant across-model disparities in their projections of not only the amplitude, but also the sign, of LL primary production. Under the stronger SSP5-8.5 forcing, with more substantial upper-ocean warming, the CMIP6 models that account for temperature-dependent remineralization promoted enhanced LL mesopelagic nutrient retention under warming, with this providing a first-order contribution to stabilizing or increasing, rather than decreasing, LL production under high emissions and low mitigation. This underscores the importance of a mechanistic understanding of mesopelagic remineralization and its sensitivity to ocean warming for predicting future ecosystem changes.

Antarctica and the Southern Ocean

Antarctica and the Southern Ocean