An official website of the United States government
Abstract Lagrangian analysis using the velocity field of the Southern Ocean State Estimate (SOSE) at 1/6° resolution quantifies the origin of the lower branch of the abyssal circulation south of 30°S. Antarctic waters from 65°S contribute 62% of the northward bottom flow at 30°S. The remaining 38% comes from deep water recirculating from sources north of 30°S. Half of this deep water is North Atlantic Deep Water, with the remainder split between Indian and Pacific Deep Waters. Deep water densifies to bottom values following several circumpolar loops, which homogenize original properties to common characteristics of Lower Circumpolar Water. Transit times of deep water starting at 30°S, arriving as abyssal waters at 30°S, are about 150 years, twice as long as transit times of waters starting near Antarctica. Paths to 30°S originating from Antarctica avoid circumpolar loops and are steered by bottom topography.
more »
« less
The International Bathymetric Chart of the Southern Ocean Version 2
Abstract The Southern Ocean surrounding Antarctica is a region that is key to a range of climatic and oceanographic processes with worldwide effects, and is characterised by high biological productivity and biodiversity. Since 2013, the International Bathymetric Chart of the Southern Ocean (IBCSO) has represented the most comprehensive compilation of bathymetry for the Southern Ocean south of 60°S. Recently, the IBCSO Project has combined its efforts with the Nippon Foundation – GEBCO Seabed 2030 Project supporting the goal of mapping the world’s oceans by 2030. New datasets initiated a second version of IBCSO (IBCSO v2). This version extends to 50°S (covering approximately 2.4 times the area of seafloor of the previous version) including the gateways of the Antarctic Circumpolar Current and the Antarctic circumpolar frontal systems. Due to increased (multibeam) data coverage, IBCSO v2 significantly improves the overall representation of the Southern Ocean seafloor and resolves many submarine landforms in more detail. This makes IBCSO v2 the most authoritative seafloor map of the area south of 50°S.
more »
« less
- Award ID(s):
- 1739003
- PAR ID:
- 10410135
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Date Published:
- Journal Name:
- Scientific Data
- Volume:
- 9
- Issue:
- 1
- ISSN:
- 2052-4463
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Previous studies suggest that meridional migrations of the Antarctic Circumpolar Current may have altered wind-driven upwelling and carbon dioxide degassing in the Southern Ocean during past climate transitions. Here, we report a quantitative and continuous record of the Antarctic Circumpolar Current latitude over the last glacial-interglacial cycle, using biomarker-based reconstructions of surface layer temperature gradient in the southern Indian Ocean. The results show that the Antarctic Circumpolar Current was more equatorward during the ice ages and shifted ~6° poleward at the end of glacial terminations, consistent with Antarctic Circumpolar Current migration playing a role in glacial-interglacial atmospheric carbon dioxide change. Comparing the temporal evolution of the Antarctic Circumpolar Current mean latitude with other observations provides evidence that Earth’s axial tilt affects the strength and latitude range of Southern Ocean wind-driven upwelling, which may explain previously noted deviations in atmospheric carbon dioxide concentration from a simple correlation with Antarctic climate.more » « less
-
Abstract The subpolar gyres of the Southern Ocean form an important dynamical link between the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. Despite their key involvement in the production and export of bottom water and the poleward transport of oceanic heat, these gyres are rarely acknowledged in conceptual models of the Southern Ocean circulation, which tend to focus on the zonally averaged overturning across the ACC. To isolate the effect of these gyres on the regional circulation, we carried out a set of numerical simulations with idealized representations of the Weddell Sea sector in the Southern Ocean. A key result is that the zonally oriented submarine ridge along the northern periphery of the subpolar gyre plays a fundamental role in setting the stratification and circulation across the entire region. In addition to sharpening and strengthening the horizontal circulation of the gyre, the zonal ridge establishes a strong meridional density front that separates the weakly stratified subpolar gyre from the more stratified circumpolar flow. Critically, the formation of this front shifts the latitudinal outcrop position of certain deep isopycnals such that they experience different buoyancy forcing at the surface. Additionally, the zonal ridge modifies the mechanisms by which heat is transported poleward by the ocean, favoring heat transport by transient eddies while suppressing that by stationary eddies. This study highlights the need to characterize how bathymetry at the subpolar gyre–ACC boundary may constrain the transient response of the regional circulation to changes in surface forcing. Significance Statement This study explores the impact of seafloor bathymetry on the dynamics of subpolar gyres in the Southern Ocean. The subpolar gyres are major circulation features that connect the Antarctic Circumpolar Current (ACC) and the coastline of Antarctica. This work provides deeper insight for how the submarine ridges that exist along the northern periphery of these gyres shape the vertical distribution of tracers and overturning circulation in these regions. These findings highlight an underappreciated yet fundamentally important topographical constraint on the three-dimensional cycling of heat and carbon in the Southern Ocean—processes that have far-reaching implications for the global climate. Future work should explore how the presence of these ridges affect the time-evolving response of the Southern Ocean to changes in surface conditions.more » « less
-
The Antarctic benthos is rich in biodiversity, with many species being endemic to the Southern Ocean. Multiple factors such as oceanic currents, glacial cycles and reproductive life stages have been attributed to the distribution of benthic dwelling invertebrates around the continent. The sea spider (Pycnogonida) Nymphon australe is a paternal brooder, which lacks a pelagic planktonic life stage. Typically brooding is assumed to suggest limited dispersal capabilities. Here we investigated the genetic structure of N. australe, a highly abundant pycnogonid species in the Southern Ocean to test assumptions of a documented circumpolar distribution. Previous studies with mitochondrial data have revealed that N. australe has high genetic diversity, limited gene flow, as well as distinct geographic structure. To resolve the phylogeographic structure of the circumpolar N. australe from the Antarctic continental shelf, we used 3RAD single nucleotide polymorphism (SNP) data from 111 individuals sampled from ten different, circumpolar geographic regions including the Western Antarctic Peninsula, Ross Sea, Weddell Sea, and Eastern Antarctica. Analyses revealed populations to have distinct regional populations with strong geographic structuring observed by locality and suggest the possibility that N. australe may be a species complex in the Southern Ocean.more » « less
-
Abstract Despite its importance for the global cycling of carbon, there are still large gaps in our understanding of the processes driving annual and seasonal carbon fluxes in the high‐latitude Southern Ocean. This is due in part to a historical paucity of observations in this remote, turbulent, and seasonally ice‐covered region. Here, we use autonomous biogeochemical float data spanning 6 full seasonal cycles and with circumpolar coverage of the Southern Ocean, complemented by atmospheric reanalysis, to construct a monthly climatology of the mixed layer budget of dissolved inorganic carbon (DIC). We investigate the processes that determine the annual mean and seasonal cycle of DIC fluxes in two different zones of the Southern Ocean—the Sea Ice Zone (SIZ) and Antarctic Southern Zone (ASZ). We find that, annually, mixing with carbon‐rich waters at the base of the mixed layer supplies DIC which is, in the ASZ, either used for net biological production or outgassed to the atmosphere. In contrast, in the SIZ, where carbon outgassing and the biological pump are weaker, the surplus of DIC is instead advected northward to the ASZ. In other words, carbon outgassing in the southern Antarctic Circumpolar Current (ACC), which has been attributed to remineralized carbon from deep water upwelled in the ACC, is also due to the wind‐driven transport of DIC from the SIZ. These results stem from the first observation‐based carbon budget of the circumpolar Southern Ocean and thus provide a useful benchmark to evaluate climate models, which have significant biases in this region.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1038/s41597-022-01366-7
