Spatial variability of surface p CO2 and air-sea CO2 flux in the Amundsen Sea Polynya, Antarctica

We report results from a yearlong, moored sediment trap in the Amundsen Sea Polynya (ASP), the first such time series in this remote and productive ecosystem. Results are compared to a long-term time series from the western Antarctic Peninsula (WAP). The ASP trap was deployed from December 2010 to December 2011 at 350 m depth. We observed two brief, but high flux events, peaking at 8 and 5 mmol C m −2 d −1 in January and December 2011, respectively, with a total annual capture of 315 mmol C m −2. Both peak fluxes and annual capture exceeded the comparable WAP observations. Like the overlying phytoplankton bloom observed during the cruise in the ASP (December 2010 to January 2011), particle flux was dominated by Phaeocystis antarctica, which produced phytodetrital aggregates. Particles at the start of the bloom were highly depleted in 13 C, indicating their origin in the cold, CO 2 -rich winter waters exposed by retreating sea ice. As the bloom progressed, microscope visualization and stable isotopic composition provided evidence for an increasing contribution by zooplankton fecal material. Incubation experiments and zooplankton observations suggested that fecal pellet production likely contributed 10-40% of the total flux during the first flux event, and could be very high during episodic krill swarms. Independent estimates of export from the surface (100 m) were about 5-10 times that captured in the trap at 350 m. Estimated bacterial respiration was sufficient to account for much of the decline in the flux between 50 and 350 m, whereas zooplankton respiration was much lower. The ASP system appears to export only a small fraction of its production deeper than 350 m within the polynya region. The export efficiency was comparable to other polar regions where phytoplankton blooms were not dominated by diatoms.

Section: Seasonality and Evolution Of The Annual Flux Eventssupporting

confidence: 69%

Particle flux on the continental shelf in the Amundsen Sea Polynya and Western Antarctic Peninsula

Ducklow

Wilson

Post

et al. 2015

“…Because these observations were coincident with supersaturated pCO 2 and low dissolved oxygen at the sea surface (Mu et al, 2014), they likely represent upwelled deep waters made buoyant by glacial meltwater. The highest subsurface glacier meltwater concentration was 2.1% and was observed at the DIS outflow (Station 60) at a depth of 82 m, i.e., just before the signal was lost to surface contamination.…”

Section: Assessing Freshwater Sourcesmentioning

confidence: 81%

Freshwater distributions and water mass structure in the Amundsen Sea Polynya region, Antarctica

Randall-Goodwin

Meredith

Jenkins

et al. 2015

Self Cite

138

We present the first densely-sampled hydrographic survey of the Amundsen Sea Polynya (ASP) region, including a detailed characterization of its freshwater distributions. Multiple components contribute to the freshwater budget, including precipitation, sea ice melt, basal ice shelf melt, and iceberg melt, from local and non-local sources. We used stable oxygen isotope ratios in seawater (d 18 O) to distinguish quantitatively the contributions from sea ice and meteoric-derived sources. Meteoric fractions were high throughout the winter mixed layer (WML), with maximum values of 2-3% (±0.5%). Because the ASP region is characterized by deep WMLs, column inventories of total meteoric water were also high, ranging from 10-13 m (±2 m) adjacent to the Dotson Ice Shelf (DIS) and in the deep trough to 7-9 m (±2 m) in shallower areas. These inventories are at least twice those reported for continental shelf waters near the western Antarctic Peninsula. Sea ice melt fractions were mostly negative, indicating net (annual) sea ice formation, consistent with this area being an active polynya. Independently determined fractions of subsurface glacial meltwater (as one component of the total meteoric inventory) had maximum values of 1-2% (±0.5%), with highest and shallowest maximum values at the DIS outflow (80-90 m) and in iceberg-stirred waters (150-200 m). In addition to these upwelling sites, contributions of subsurface glacial meltwater could be traced at depth along the ~ 27.6 isopycnal, from which it mixes into the WML through various processes. Our results suggest a quasi-continuous supply of melt-laden iron-enriched seawater to the euphotic zone of the ASP and help to explain why the ASP is Antarctica's most biologically productive polynya per unit area.

“…Variability in the import of thick multi-year sea ice from the southern Bellingshausen Sea into the eastern Amundsen Sea, together with variability in the number of icebergs on the outer continental shelf that retain summer sea ice, were other factors contributing to PIP/ASP variability. The sPIP and eASP sea ice changes are important, as they affect the timing, duration and size of these two polynyas and thus impact this biologically productive area (Arrigo and van Dijken, 2003;Arrigo et al, 2012;Alderkamp et al, 2015;Mu et al, 2015), as well as possibly indicating a response to changes in heat and freshwater inputs (Randall-Goodwin et al, 2015;Sherrell et al, 2015).…”

Section: Discussionmentioning

confidence: 99%

Seasonal sea ice changes in the Amundsen Sea, Antarctica, over the period of 1979–2014

Stammerjohn

Maksym

Massom

et al. 2015

Self Cite

Recent attention has focused on accelerated glacial losses along the Amundsen Sea coast that result from changes in atmosphere and ocean circulation, with sea ice playing a mediating but not well-understood role. Here, we investigated how sea ice has changed in the Amundsen Sea over the period of 1979 to 2014, focusing on spatio-temporal changes in ice edge advance/retreat and percent sea ice cover in relation to changes in winds. In contrast to the widespread sea ice decreases to the east and increases to the west of the Amundsen Sea, sea ice changes in the Amundsen Sea were confined to three areas: (i) offshore of the shelf break, (ii) the southern Pine Island Polynya, and (iii) the eastern Amundsen Sea Polynya. Offshore, a 2-month decrease in ice season duration coincided with seasonal shifts in wind speed and direction from March to May (relating to later ice advance) and from September to August (relating to earlier retreat), consistent with reported changes in the depth/location of the Amundsen Sea Low. In contrast, sea ice decreases in the polynya areas corresponded to episodic or step changes in spring ice retreat (earlier by 1-2 months) and were coincident with changes to Thwaites Iceberg Tongue (located between the two polynyas) and increased southeasterly winds. Temporal correlations among these three areas were weak, indicating different local forcing and/or differential response to large-scale forcing. Although our analysis has shown that part of the variability can be explained by changes in winds or to the coastal icescape, an additional but unknown factor is how sea ice has responded to changes in ocean heat and freshwater inputs. Unraveling cause and effect, critical for predicting changes to this rapidly evolving ocean-ice shelf-sea ice system, will require in situ observations, along with improved remote sensing capabilities and ocean modeling.