Date of Award

Fall 2020

Project Type

Thesis

Program or Major

Oceanography

Degree Name

Master of Science

First Advisor

Jennifer L Miksis-Olds

Second Advisor

Thomas C Lippmann

Third Advisor

Josef M Jech

Abstract

Interannual variability of ocean temperatures and sea ice extent has been observed on the eastern Bering Sea (EBS) shelf, where annual conditions have resulted in regional “Cold” or “Warm” years. Consecutive years of Cold or Warm year characterization has resulted in regime states within the past two decades. A characteristic feature of the EBS is a subsurface layer linked to seasonal sea ice (SSI) and defined by bottom temperatures less than 2°C, termed the Cold Pool. Cold Pool variability is tied to the dynamics of fish distribution in the Arctic and subarctic ecotones. Water column, multifrequency acoustic backscatter data were collected remotely using upward looking echosounders along the EBS shelf from 2008-2018. Acoustic data were coupled with additional bottom temperature, regional SSI, and local SSI data from the Cold regime between 2006-2013 and the Warm regime from 2014-2018 to assess the relationship between zooplankton communities and Cold Pool variation. Water column averaged area backscatter was two orders of magnitude greater during the Cold regime than during the Warm regime coupled with early ice edge receding. Multifrequency acoustic analysis indicated a shift in the Warm regime zooplankton communities from larger to smaller bodied species on the EBS shelf resulting in a change in the average acoustic abundance. Cold Pool proxy regional SSI was a better predictor variable for zooplankton abundance than bottom temperature in the Cold regime, while Warm regime bottom temperature and regional SSI were equal in predictive power and resulted in improved predictive model performance. Although the predictive models did not capture the dynamics of the regime shift in 2013, the Cold regime exhibited increased stochasticity in bottom temperature, SSI, and acoustic backscatter prior to the shift. Regime shift early warning signals from further mining of acoustic and environmental data warrant exploration for comprehensive management practices in the Bering Sea and neighboring Arctic ecosystems.

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