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Open Access

Degree Program


Degree Type

Master of Science (M.S.)

Year Degree Awarded


Month Degree Awarded



Sea ice, climate, proxy, Arctic, diatom


Seasonal sea ice is an important component of the global climate system. Sea ice influences exchange rates of heat, moisture, and gas between the ocean and atmosphere. Sea ice also plays critical roles in high latitude ecosystems and marine carbon cycling. Records of sea-ice extent and duration in the Arctic Ocean and its marginal seas through geologic time are valuable resources for better understanding the intricate relationships between sea ice and climate.

IP25, a compound biosynthesized exclusively by diatoms associated with sea ice, has been used to construct qualitative records of sea ice from sediment cores in some areas of the Arctic. However, IP25 has not previously been applied to sediments from the Bering and Chukchi Seas. This area exhibits a wide range of interannual seasonal ice duration, which makes the region a promising natural laboratory for developing a quantitative core-top calibration between sea ice and the IP25 biomarker.

A sample suite of surface sediments from the Bering and Chukchi Seas representing a range of latitudes (60-72o N) and durations of sea ice per year (0.5-11 months/year) are analyzed for this study. Gas chromatography/mass spectrometry analysis of sediment solvent extracts reveals the presence of IP25 in all samples and higher IP25 concentrations in the Chukchi Sea compared to in the Bering Sea. IP25 concentrations are compared with data for several sea surface conditions: mean annual sea-ice duration, sea surface temperature and salinity, and insolation data. An exponential relationship between TOC-normalized IP25 concentration and average annual duration of sea ice is identified. Negative exponential relationships are identified between IP25 and the other sea surface conditions: average annual and August sea surface temperature and average annual and August sea surface salinity. Exponential relationships are also identified between TOC-normalized IP25 concentrations and insolation, and insolation coupled with sea-ice concentration.

IP25 in surface sediments is a viable quantitative proxy for sea-ice duration in the Bering and Chukchi Seas. However, sea surface conditions, such as temperature, salinity, sea-ice duration/concentration, and insolation are not independent variables. Therefore it is difficult to determine which of these environmental factors has/have the most influence on IP25 production. Further research and statistical analysis may serve to refine these relationships.

First Advisor

Julie Brigham-Grette

Second Advisor

Steven T. Petsch