T114 Polar Paleobiology and Paleoenvironmental Proxies

Wednesday, 28 October 2020
10:00 AM - 12:00 PM
Meeting Rooms

OXYGEN AND CARBON ISOTOPES IN ADAMUSSIUM COLBECKI: δ13C PROXY FOR SEA-ICE PERSISTENCE?

Paper number: T114-7
Program: Technical Sessions
Time: 11:20 AM – 11:35 AM

Authors

Abstract

The Antarctic scallop Adamussium colbecki is a promising proxy for sea-ice persistence and can potentially resolve subannual seawater conditions characteristic of annual and multiannual sea ice. Alternating groups of widely- and narrowly-spaced striae (small ridges on valve surfaces) are thought to indicate seasonal growth differences: wide groups in summer, narrow groups in winter. Shell oxygen (δ18Os) and carbon (δ13Cs) in striae groups may therefore reflect seasonal seawater conditions. We expect lower δ18Os in wide summer striae groups under both annual and multiannual sea ice if glacial meltwater mixes through the water column. We also expect higher δ13Cs in wide striae groups under annual sea ice but not under multiannual sea ice, as phytoplankton blooms post sea-ice breakout enrich seawater δ13CDIC.

Scallops were collected from two sites in western McMurdo Sound (Ross Sea) located ~30 km apart: Explorers Cove (EC) has multiannual sea ice and Bay of Sails (BOS) has annual sea ice. Adults were collected live by divers at 9–18 m depth in 2008 from EC and BOS. Additional juveniles (< 2 yrs) were collected from EC in 2016. Two adults each from EC and BOS and two 2016 juveniles were serially sampled for stable isotopes. δ13Cs decreases over ontogeny due to metabolic effects; the linear trend was removed to enable seasonal comparison. Detrended residuals are referred to as δ13Cs det.

Mean δ18Os (~3.7‰) is not different in narrow and wide striae groups under either annual or multiannual sea ice, suggesting negligible glacial meltwater mixing at depth and minimal seasonal temperature change at both sites. δ18Os values are within expected equilibrium range and decrease over ontogeny, suggesting increased growth during warmer temperatures in older scallops. In contrast, mean δ13Cs det is ~1‰ higher in wide summer striae groups than narrow winter striae groups under annual sea ice at BOS, but not different between striae groups under multiannual sea ice in EC adults. δ13Cs det is also higher in wide summer striae groups from 2016 EC juveniles, however sea ice broke out at EC in 2015, so juveniles experienced annual-like sea-ice conditions. Seasonal differences in δ13Cs suggest that carbon isotopes coupled with striae width in A. colbecki may be a good proxy for sea-ice persistence in Antarctica both in modern and fossil assemblages.

Geological Society of America Abstracts with Programs. Vol. 52, No. 6

doi: 10.1130/abs/2020AM-357341

© Copyright 2020 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.