Past Sea Ice State in McMurdo Sound, Antarctica, from Oxygen, Carbon and Nitrogen Stable Isotopes and Growth Striations in the Antarctic Scallop Adamussium Colbecki

• Main Author: Puhalski, Emma
• Format: Text
• Language: unknown
• Published: Union | Digital Works 2022
• Subjects: Paleoclimate; sea ice; Antarctica; Holocene; Adamussium colbecki; scallop; Paleobiology; Antarctic; Bay of Sails; Explorers Cove; McMurdo Sound; The Antarctic; Antarc*; Sea ice
• Online Access: https://digitalworks.union.edu/theses/2668; https://digitalworks.union.edu/cgi/viewcontent.cgi?article=3719&context=theses

Fluctuations in sea ice cover are major factors driving climate change and are a substantial component of the global climate feedback loop. Antarctica currently lacks notable proxy records of sea ice state; bivalves archive environmental conditions and can be studied to track changes in sea ice cover through time. Adamussium colbecki is a large sea scallop with a circum-Antarctic distribution and an abundant fossil record throughout the Holocene. Our group’s work shows that carbon (d13Cs) and nitrogen (d15NCBOM) isotopes in modern scallop shells record seasonal variation in sea ice state over time when paired with growth markers called striae. We also found that sea ice cover is recorded by low d13Cs values in narrow striae while ice-free conditions are recorded by high d13Cs values in wide striae. Nitrogen isotopes of carbonate bound organic material also recorded sea ice state, with ice-free conditions recorded by lower values. Here we apply these paleoclimate proxies by analyzing A. colbecki subfossil shells collected from terraces along Explorers Cove (EC) and Bay of Sails (BOS), western McMurdo Sound, Antarctica which grew between 1,200 and 4,000 years ago (based on 14C ages). Today, these two sites have contrasting sea ice states: persistent (multiannual) sea ice at EC and annual sea ice (that melts out every year) at BOS. Two adult fossil shells collected at EC and four fossil shells (including one juvenile) collected at BOS were serially sampled for d13C, d18O, and d15N from the growing shell margin to the umbo. Imaging of striae allowed for d13Cs and d18Os values to be paired with summer (wide striae) and winter (narrow striae) scallop growth; d15NCBOM required larger sample size, so were not seasonally paired. Seawater temperature proxy records suggest warmer conditions 2,000-5,000 yr BP, so we expect variable d13Cs values recording annual sea ice in shells from both sites. Modern carbon and nitrogen isotopes in Adamussium colbecki shells agree with known sea ice conditions and can be considered an ...