Cecilia Peralta-Ferriz

Changing Arctic Ocean freshwater pathways

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomalyof the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High—a characteristic peak in sea level atmospheric pressure—which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content. Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.

Arctic Ocean Circulation Patterns Revealed by GRACE

AbstractMeasurements of ocean bottom pressure (OBP) anomalies from the satellite mission Gravity Recovery and Climate Experiment (GRACE), complemented by information from two ocean models, are used to investigate the variations and distribution of the Arctic Ocean mass from 2002 through 2011. The forcing and dynamics associated with the observed OBP changes are explored. Major findings are the identification of three primary temporal–spatial modes of OBP variability at monthly-to-interannual time scales with the following characteristics. Mode 1 (50% of the variance) is a wintertime basin-coherent Arctic mass change forced by southerly winds through Fram Strait, and to a lesser extent through Bering Strait. These winds generate northward geostrophic current anomalies that increase the mass in the Arctic Ocean. Mode 2 (20%) reveals a mass change along the Siberian shelves, driven by surface Ekman transport and associated with the Arctic Oscillation. Mode 3 (10%) reveals a mass dipole, with mass decreasing ...

The Dominant Role of the East Siberian Sea in Driving the Oceanic Flow Through the Bering Strait—Conclusions From GRACE Ocean Mass Satellite Data and In Situ Mooring Observations Between 2002 and 2016

It is typically stated that the Pacific-to-Arctic oceanic flow through the Bering Strait (important for Arctic heat, freshwater, and nutrient budgets) is driven by local wind and a (poorly defined) far-field “pressure head” forcing, related to sea surface height differences between the Pacific and the Arctic. Using monthly, Arctic-wide, ocean bottom pressure satellite data and in situ mooring data from the Bering Strait from 2002 to 2016, we discover the spatial structure of this pressure head forcing, finding that the Bering Strait throughflow variability is dominantly driven from the Arctic, specifically by sea level change in the East Siberian Sea (ESS), in turn related to westward winds along the Arctic coasts. In the (comparatively calm) summer, this explains approximately two thirds of the Bering Strait variability. In winter, local wind variability dominates the total flow, but the pressure head term, while still correlated with the ESS-dominated sea level pattern, is now more strongly related to Bering Sea Shelf sea level variability.

Proxy representation of Arctic Ocean bottom pressure variability: Bridging gaps in GRACE observations

Using time-varying ocean bottom pressure (OBP) from the Gravity Recovery and Climate Experiment (GRACE), a 9-year in situ OBP record at the North Pole, and wind reanalysis products, we perform a linear regression analysis to identify primary predictor time series that enable us to create a proxy representation of the Arctic time-varying OBP that explains the largest fraction of the observed Arctic OBP variability. After cross-validation, two predictors – North Pole OBP record, and wind-OBP coupling from maximum covariance analysis – explain 50% of the total variance of the Arctic OBP. This work provides a means for bridging existing short gaps in GRACE measurements, and potentially longer future gaps that may result if GRACE and its follow-on mission do not overlap. The technique may be applicable to bridge gaps in GRACE measurements in other oceanic regions.