The ocean coastal‐shelf‐slope ecosystem west of the Antarctic Peninsula (WAP) is a biologically productive region that could potentially act as a large sink of atmospheric carbon dioxide. The duration of the sea‐ice season in the WAP shows large interannual variability. However, quantifying the mechanisms by which sea ice impacts biological productivity and surface dissolved inorganic carbon (DIC) remains a challenge due to the lack of data early in the phytoplankton growth season. In this study, we implemented a circulation, sea‐ice, and biogeochemistry model (MITgcm‐REcoM2) to study the effect of sea ice on phytoplankton blooms and surface DIC. Results were compared with satellite sea‐ice and ocean color, and research ship surveys from the Palmer Long‐Term Ecological Research (LTER) program. The simulations suggest that the annual sea‐ice cycle has an important role in the seasonal DIC drawdown. In years of early sea‐ice retreat, there is a longer growth season leading to larger seasonally integrated net primary production (NPP). Part of the biological uptake of DIC by phytoplankton, however, is counteracted by increased oceanic uptake of atmospheric CO2. Despite lower seasonal NPP, years of late sea‐ice retreat show larger DIC drawdown, attributed to lower air‐sea CO2fluxes and increased dilution by sea‐ice melt. The role of dissolved iron and iron limitation on WAP phytoplankton also remains a challenge due to the lack of data. The model results suggest sediments and glacial meltwater are the main sources in the coastal and shelf regions, with sediments being more influential in the northern coast.
The west Antarctic Peninsula (WAP) is a region of marked climatic variability, exhibiting strong changes in sea ice extent, retreat of most of its glaciers, and shifts in the amount and form of precipitation. These changes can have significant impacts on the oceanic freshwater budget and marine biogeochemical processes; it is thus important to ascertain the relative balance of the drivers and the spatial scales over which they operate. We present a novel 7‐year summer‐season (October to March; 2011 to 2018) series of oxygen isotopes in seawater (δ18O), augmented with some winter sampling, collected adjacent to Anvers Island at the WAP. These data are used to attribute oceanic freshwater changes to sea ice and meteoric sources, and to deduce information on the spatial scales over which the changes are driven. Sea ice melt shows significant seasonality (∼9% range) and marked interannual changes, with pronounced maxima in seasons 2013/14 and 2016/17. Both of these extrema are driven by anomalous winds, but reflect strongly contrasting dynamic and thermodynamic sea ice responses. Meteoric water also shows seasonality (∼7% range) with interannual variability reflecting changes in the input of accumulated precipitation and glacial melt to the ocean. Unlike sea ice melt, meteoric water extremes are especially pronounced in thin (<10 m) surface layers close to the proximate glacier, associated with enhanced ocean stratification. Isotopic tracers help to deconvolve the complex spatio‐temporal scales inherent in the coastal freshwater budget, and hence improve our knowledge of the separate and cumulative physical and ecological impacts.
more » « less- Award ID(s):
- 2026045
- NSF-PAR ID:
- 10445921
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Oceans
- Volume:
- 126
- Issue:
- 6
- ISSN:
- 2169-9275
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
more » « less
Abstract -
more » « less
Abstract The Southern Ocean is chronically undersampled due to its remoteness, harsh environment, and sea ice cover. Ocean circulation models yield significant insight into key processes and to some extent obviate the dearth of data; however, they often underestimate surface mixed layer depth (MLD), with consequences for surface water‐column temperature, salinity, and nutrient concentration. In this study, a coupled circulation and sea ice model was implemented for the region adjacent to the West Antarctic Peninsula, a climatically sensitive region which has exhibited decadal trends towards higher ocean temperature, shorter sea ice season, and increasing glacial freshwater input, overlain by strong interannual variability. Hindcast simulations were conducted with different air‐ice drag coefficients and Langmuir circulation parameterizations to determine the impact of these factors on MLD. Including Langmuir circulation deepened the surface mixed layer, with the deepening being more pronounced in the shelf and slope regions. Optimal selection of an air‐ice drag coefficient also increased modeled MLD by similar amounts and had a larger impact in improving the reliability of the simulated MLD interannual variability. This study highlights the importance of sea ice volume and redistribution to correctly reproduce the physics of the underlying ocean, and the potential of appropriately parameterizing Langmuir circulation to help correct for biases towards shallow MLD in the Southern Ocean. The model also reproduces observed freshwater patterns in the West Antarctic Peninsula during late summer and suggests that areas of intense summertime sea ice melt can still show net annual freezing due to high sea ice formation during the winter.
-
more » « less
Abstract The Southern Ocean plays an important role in the uptake of atmospheric CO2. In seasonally ice‐covered regions, estimates of air‐sea exchange remain uncertain in part because of a lack of observations outside the summer season. Here we present new estimates of air‐sea CO2flux in the West Antarctic Peninsula (WAP) from an autonomous mooring on the continental shelf. In summer, the WAP is a sink for atmospheric CO2followed by a slow return to atmospheric equilibrium in autumn and winter. Outgassing is almost entirely suppressed by ice cover from June through October, resulting in a modest net annual CO2sink. Model projections indicate sea ice formation will occur later in the season in the coming decades potentially weakening the net oceanic CO2sink. Interannual variability in the WAP is significant, highlighting the importance of sustained observations of air‐sea exchange in this rapidly changing region of the Southern Ocean.
-
Satellite images from Antarctica reveal important changes in the coastal icescape (fast-ice, icebergs and ice shelves) but these yearly changes and their impacts on the coastal circulation and ice shelf basal melt rates are not represented in the Earth System Models used to project future sea level rise. The impacts of these yearly icescape changes are thus investigated using a high-resolution regional ocean-ice shelves-sea ice coupled model of the Amundsen Sea (Antarctica). A set of nine semi-idealized experiments were designed to highlight the impacts of (a) the collapse of the Thwaites Glacier Tongue, (b) the disappearance of the Bear Ridge Iceberg Chain and tabular iceberg B22, and (c) presence/absence of a fast-ice cover between Thwaites and Pine Island ice shelves, in both cold and warm background hydrological conditions. The dataset features the results of the nine experiments and reveals changes in sea ice concentrations, coastal oceanic circulation and oceanic heat supply to the ice shelf cavities, ice shelf basal melt rates, hydrological conditions, and fluxes of heat/freshwater at the sea surface. These model results are archived in self-documented NetCDF files with the appropriate metadata for each variable. The dataset includes a 'readme file' providing an overview of the archive as well as additional information regarding the model results.more » « less
-
more » « less
Abstract Low‐frequency (Interannual and longer timescale) variability in sea surface temperature (SST) of the Indian Ocean plays a crucial role in affecting the regional climate. Using a high‐resolution global model simulation, we show that internal oceanic variability is an important cause of the observed low‐frequency variability in the subtropical‐midlatitude south Indian Ocean (SIO) between 20° and 40°S, a marked southward shift in the latitude band of active internal variability for the low‐frequency compared to earlier estimates based on coarser Indian Ocean regional models. Notably, we show that internal variability does not contribute to the observed low‐frequency variability in the Seychelles−Chagos thermocline ridge region. Energy budget analysis shows that baroclinic instability is the primary cause for the internal variability. The slowly growing baroclinic instabilities at low frequency and longer length scale favor Rossby waves' generation, propagating the SST and sea level anomaly signals westward.
