Sinking particle flux in the sea ice zone of the Amundsen Shelf, Antarctica

Abstract

a b s t r a c tWe have examined the flux, biogenic composition, and isotopic values of sinking particles collected by a time-series sediment trap deployed in the sea ice zone (SIZ) of the Amundsen Sea from January 2011 for 1 year. The major portion of the particle flux occurred during the austral summer in January and February when sea ice concentration was reduced to o 60%. Biogenic components, dominated by opal ( $ 78% of the biogenic components), accounted for over 75% of particle flux during this high-flux period. The dominant source of sinking particles shifted from diatoms to soft-tissued organisms, evidenced by high particulate organic carbon (POC) content ( 430%) and a low bio-Si/POC ratio (o 0.5) during the austral winter. CaCO 3 content and its contribution to total particle flux was low ( $ 6%) throughout the study period. Aged POC likely supplied from sediment resuspension accounted for a considerable fraction only from October to December, which was evidenced by a low radiocarbon content and relatively high (30-50%) content of the non-biogenic components. When compared with POC flux inside the Amundsen Sea polynya obtained by the US Amundsen Sea Polynya International Research Expedition (ASPIRE), the POC flux integrated over the austral summer in the SIZ was virtually identical, although the maximum POC flux was approximately half that inside the Amundsen Sea polynya. This comparatively high POC flux integrated over the austral summer in the SIZ may be caused by phytoplankton blooms persisting over a longer periods and more efficient export of organic matter potentially owing to the diatom-dominant plankton community. If this observation is a general phenomenon on the Amundsen Shelf, the role of the SIZ, compared with the polynyas, need to be examined more carefully when trying to characterize the POC export in this region.

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

“…Kim et al (2014) observed an annual POC flux similar to ours at a site 250 km to the northwest, in the sea ice zone outside the ASP, an area covered by sea ice throughout the year. Primary production in the SIZ region averaged 17 mmol C m −2 d −1 in December 2010 and January 2011 (Lee et al, 2012), about 10% of the values inside the ASP.…”

“…Indeed, ASPIRE observations of high POC inventories and large krill populations associated with marginal sea ice Station 66 on the northern edge of the ASP (Wilson et al, 2015;Yager et al, 2014) may offer insight for the springtime flux we observed the following year. Kim et al (2014) present sediment trap observations overlapping ours in time, but from the zone of persistent 40-100% sea ice cover 250 km northwest of the central ASP (Figure 1). They observed one peak in early 2011, but did not see a second peak at the end of the year.…”

“…One explanation for this contrast is that some of the particle flux in the surrounding SIZ region could have been derived from the high productivity central ASP. However Kim et al (2014) argue on the basis of sample composition that the material was derived from locally-produced, rapidly-sinking particles, and not advected from the central ASP. Weston et al (2013) reported a large difference between surface production and trap flux at 200 m for a moored (conical-type) sediment trap deployed in [2005][2006] in Marguerite Bay (67.56°S, 68.23°W), 350 km south of the WAP trap.…”

“…They did not observe the highly depleted carbon isotopic values that we observed (−26.1 to −27.9), possibly indicating the lack of an intense phytoplankton bloom in the SIZ region. Because Kim et al (2014) employed a conical trap (the same as our WAP trap), the absence of a second peak may be explained by collection bias and/or lateral advection.…”

The interdisciplinary marine system of the Amundsen Sea, Southern Ocean: Recent advances and the need for sustained observations

“…Although the export and NCP fractions were typical of other ocean ecosystems (Henson et al, 2012), only about 1% of the export flux leaving the upper 50-100 meters survived to be captured in moored sediment traps at 350-400 meters Kim et al, 2015). Organic degradation in the Amundsen shelf sediment measured by oxygen consumption (aerobic respiration) and sulfate reduction (anaerobic) accounted for only about 1% of the primary production in the surface water (Kim, S.H.…”