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Growth Analysis of Saxidomus gigantea as a Proxy for Seasonal Sea Ice Flux

Session: Timestamped Biomineralized Structures in Coastal Environmental Monitoring and Cultural Research

Presenting Author:

Freya Cordell

Authors:

Cordell, Freya¹, Andrus, C. Fred T.², Bassett, Christine N.³, West, Catherine F⁴

(1) Geological Sciences, University of Alabama, Tuscaloosa, AL, USA, (2) Geological Sciences, University of Alabama, Tuscaloosa, AL, USA, (3) Geological Sciences, University of Alabama, Tuscaloosa, AL, USA, (4) Archaeology, Boston University, Boston, MA, USA,

Abstract:

The discovery of vertebrate zooarchaeological remains of ice-dependent species in the Aleutian Islands has provoked arguments that seasonal sea ice reached the southern Bering sea during the late Holocene. However, this is significantly farther south than sea ice has been otherwise documented to occur. This project utilizes sclerochronology of ancient and modern samples of butter clam (Saxidomas gigantea) from Dutch Harbor, Unalaska Island, AK, USA to estimate past seasonality and assess the possibility of late-Holocene sea ice. This species displays growth increments bracketed by lines indicating cessation that occur when the temperature is below ~5°C. Oxygen isotope analysis can confirm that the growth cessations occurred due to winter temperatures rather than another cause. Measuring the distance between winter cessation lines of modern and ancient samples allows comparison of growth season length. Measurements from samples from three mid to late Holocene archaeological sites were compared to data from nearby modern clams. Seasonal sea ice formation would presumably be associated with shorter growing seasons than those measured in ice free periods. However, data indicate that the late Holocene samples have similar and occasionally longer growth seasons compared to the modern clams. If these data are verified through lunar-daily microincrement counts, these results will necessitate new hypotheses as to what could have caused ice-dependent species to shift their habitats to the Aleutian islands. The synthesis of paleoclimate data such as these is useful to understanding historical baseline ice extent to better understand how present anthropogenic warming is causing sea ice loss.