Date of Award
12-2025
Document Type
Thesis
Degree Name
Master of Science (MS)
Degree Statement
Master of Science in Atmospheric Sciences
Department
Department of Atmospheric Sciences
Committee Chair
Polyakov, Igor
Committee Member
Bhatt, Uma
Committee Member
Pnyushkov, Andrey
Table of Contents
Chapter 1: Introduction.
1.1 Arctic climate change and amplification
1.2 Role of surface freshwater in the Arctic
1.3 Eurasian Basin and Siberian freshwater sources
1.4 Open questions in Eurasian Basin freshwater dynamics
Chapter 2: Data and methodology.
2.1 Data
2.1.1 Oceanic data
2.1.2 River discharge data
2.1.2 Reanalyses data
2.2 Methods
2.2.1 Defining the timing and vertical extent of the freshening event
2.2.2 Seasonal analysis
2.2.3 Quantifying ocean response
2.2.4 Techniques for freshwater source and pathway identification
Chapter 3: Results.
3.1 Documenting the 2015-2017 freshening event
3.2 Sources and drivers of the 2015-2017 freshening
3.2.1 Impact of cross-slope advection
3.2.2 Kara Sea as a driver of salinity change
3.3 Consequences of the eastern Eurasian Basin freshening on ocean currents
Chapter 4: Discussion and conclusions.
4.1 Summary of findings
4.2 Broader climate implications
4.3 Uncertainties and limitations
4.4 Conclusions
References.
Abstract
The Arctic Ocean is undergoing rapid change, with freshwater playing a central role in shaping stratification, vertical heat exchange, and sea-ice loss. Using long-term observations from the Nansen and Amundsen Basins Observational System (NABOS), we document an extreme freshening event in the eastern Eurasian Basin between late 2015 and early 2017. During this period, salinity in the upper 175 m decreased by ~0.5 psu, equivalent to an additional ~0.6 m of freshwater, relative to the preceding (2013-2015) and following (2017-2018) years. The anomaly originated on the Kara Sea shelves in 2014-2015, when exceptional Yenisey and Ob discharge provided a combined freshwater surplus of ~0.78 m, sufficient to explain the observed freshening. Trajectory analysis traced the freshwater anomaly to the Kara Sea, with transport times of 8-9 months to the shelf and 22-23 months to offshore. The resulting enhanced stratification suppressed upper-ocean currents by ~22% and vertical shear by ~50%, reducing vertical heat flux from the ocean interior. These changes enabled thicker sea ice to persist through the summers of 2016-2017, in contrast to near-ice-free conditions in adjacent years. While wind anomalies aided the retention of freshwater along the slope, river discharge was the dominant driver of the event. Overall, the 2015-2017 event demonstrates how episodic river discharge can restructure upper-ocean stratification, reduce oceanic heat fluxes, and lead to delayed melt and increased summer sea ice, highlighting the sensitivity of upper-ocean processes and sea ice to episodic freshwater forcing in the Arctic.
Recommended Citation
More, Dolly, "Documenting the 2015-2017 freshening of the eastern Eurasian Basin of the Arctic Ocean and evaluating its drivers and consequences" (2025). Atmospheric Sciences. 79.
https://scholarworks.alaska.edu/uaf_grad_atmospheric/79