Variability and Trends of the Alaska Gyre From Argo and Satellite Altimetry

Abstract

The interannual variability and trends of the Alaska Gyre and Gulf of Alaska (GOA) circulation are examined using meridional geostrophic transport from Argo temperature and salinity (2004–2017) and altimetric sea surface height (1993–2017). More than half of the top 1,500 m meridional transport variability in the Alaska Gyre is accounted for by a statistical mode strongly correlated with the Pacific Decadal Oscillation (PDO) index, consistent with the PDO exerting a major influence on North Pacific sea surface temperature variability. During a positive phase of the PDO, the zero‐transport streamline separating the subtropical from the Alaska Gyre is shifted to the south from its mean position, while more transport is diverted northward, associated with a stronger and larger Alaska Gyre. Additionally, over the 25‐year altimetric record there is a linear, increasing trend in strength of the Alaska Gyre (but not in areal extent), accompanied by an increasing trend for the incoming North Pacific Current. The effect of the PDO transport mode on GOA circulation is weak. Temperature and salinity volume averaged for the GOA covary with the PDO index, with warmer and fresher waters during a positive phase. Despite correlated anomalies for temperature, salinity, and northward transport into the GOA, however, geostrophic advection from the south contributes only minimally to the interannual variations of water properties in the GOA. An exception was the marine heat wave of 2013/2014 and its aftermath when temperature advection from the south played a more appreciable role for warming and subsequent cooling of the GOA.

Drivers of Marine Heatwaves in the East China Sea and the South Yellow Sea in Three Consecutive Summers During 2016–2018

“…analysis on different time scales (Asbjørnsen et al, 2019;Bond et al, 2015;Fathrio et al, 2017;Feng et al, 2008;Hristova et al, 2019;T. Lee et al, 2004;Zhang et al, 2018).…”

“…The residuals (Adv_res) in Equation 2 may come from the interpolation errors from unstructured grids into the regular boundaries. The advection decomposition has been widely used in heat budget 10.1029/2020JC016518 Journal of Geophysical Research: Oceans analysis on different time scales (Asbjørnsen et al, 2019;Bond et al, 2015;Fathrio et al, 2017;Feng et al, 2008;Hristova et al, 2019;T. Lee et al, 2004;Zhang et al, 2018).…”

Monthly to Decadal Variability of Mesoscale Stirring in the California Current System: Links to Upwelling, Climate Forcing, and Chlorophyll Transport

“…Seasonally, transport to the CCS from the NPC is greatest in August and September and weakest in January‐February (Hristova et al., 2019). Seasonal fluctuations of the relative flow of the NPC into the CCS versus the AC match well with the seasonal FSLE intensity data: greater flow from the NPC into the CCS corresponds with the time period of greatest FSLE intensity and spatial extent, while greater flow into the AC relative to the CCS corresponds with the time period of lowest FSLE intensity and spatial extent in the CCS.…”

Spatio-temporal persistence of zooplankton communities in the Gulf of Alaska

“…The Alaska Current is the primary oceanographic feature in our study area, and weak circulation of the current in the Subarctic gyre has been previously associated with warmer and more stratified conditions [ 65 ], reducing primary productivity and fisheries yields [ 66 ]. While variability in the strength and timing of North Pacific hydrography ultimately derives from atmospheric pressure systems in the North Pacific, the flow of the Alaska Current has now been shown to also vary with the latitudinal position of the North Pacific Current where the Alaskan Current diverges northward, and the Pacific Decadal Oscillation [ 67 ]. Intriguingly, in our study this region off coastal Vancouver Island was also the most variable region in terms of zooplankton community persistence, even within temperature regimes.…”