Anomalous eddy heat and freshwater transport in the Gulf of Alaska

Abstract

Characteristics of eddies in the Gulf of Alaska are assessed from January 2003 through April 2012. Ensemble statistics for eddy subsurface water properties on isopycnals are computed using temperature and salinity profiles from Argo profiling floats located within eddies, which are identified in sea-surface height using objective techniques. Ninety cyclonic and 154 anticyclonic eddies are identified during this period. The anticyclonic eddies are strongly nonlinear and exhibit significant warm subsurface temperature anomalies and associated salty anomalies on isopycnals while no clear distinguishing subsurface anomalies on isopycnals are detected in association with the cyclonic eddies. Heat and freshwater fluxes for the eddies are estimated from integrations in depth coordinates. The anticyclonic eddies transport heat both westward off the continental shelf into the Subarctic Gyre and westward within the Alaskan Stream. However, they transport salt into the Subarctic Gyre and freshwater within the Alaskan Stream. In both pathways eddy heat and freshwater transport show possible year-to-year fluctuations, varying from 0 to 50.4 3 10 18 J a 21 and 216.8 to 17.4 km 3 a 21 , respectively. The anticyclonic eddies are capped by relatively fresh water yearround.

Zonal evolution of Alaskan Stream structure and transport quantified with Argo data

“…Though our full‐depth estimates are generally higher than those found in the literature, most of these prior estimates fall within (or very close to) our 5%–95% confidence bounds (Figure ). We expect some differences between our long‐term mean values of the transport and those derived from shorter records given the strong variability of this current on weekly to interannual timescales and the influence of strong mesoscale eddies [ Musgrave et al ., ; Crawford et al ., ; Ueno et al ., ; Stabeno and Hristova , ; Lyman and Johnson , ]. The slight dip in transport seen at 170°W may be due to the presence of significant passes close to this location (e.g., Samalga and Amutka passes) through which some AS water can flow into the Bering Sea.…”

“…Anticyclonic eddies tend to dominate the eddy field within the AS and typically form near Sitka, Yakutat, or the Kenai Peninsula. They slowly (mean velocity ∼2 km day −1 ) carry warm, salty anomalies southwestward along the shelf break and thereby contribute significantly to the heat and freshwater transports out of the Alaskan shelf region [ Ueno et al ., ; Lyman and Johnson , ]. These eddies are a potential source of noise when estimating mean transports or conditions.…”

Seaglider surveys at Ocean Station Papa: Circulation and water mass properties in a meander of the North Pacific Current

“…The thermal stratification at 150 m is too weak for this maximum to be accounted for solely by vertical displacement of isopycnals, implying a change along isopycnals, as observed by Seagliders. Although the warm mode , and associated downward isopycnal displacement, is suggestive of North American coastal water sometimes transported to OSP by anticyclonic eddies [ Crawford et al ., ; Whitney et al ., ; Lyman and Johnson , ], warm mode water also had elevated oxygen concentrations along isopcynals in the lower halocline. This is evidence against the interpretation of the warm mode as coastal water, since coastally generated anticyclones in the GOA contain oxygen‐poor water sourced from the diluted signature of equatorial water found along the North American continental slope [ Aydin et al ., ; Castro et al ., ; Crawford et al ., ; Thomson and Krassovski , ].…”

“…Currents are weak near OSP in the low‐energy GOA, though mesoscale eddies and meanders are nevertheless ubiquitous, and the ratio of eddy kinetic energy to mean kinetic energy in the eastern GOA is comparable to other regions in the North Pacific Ocean [ Thomson et al ., ; Paduan and Niiler , ]. Eddies formed from instabilities or flow‐topography interaction along the North American continental margin transport coastal water and associated nutrient, heat, and freshwater signatures seaward away from the eastern gyre boundary [e.g., Crawford et al ., ; Pelland et al ., ; Lyman and Johnson , ], but likely do not account for all of the eddying motions in the gyre interior [ Thomson et al ., ; Chelton et al ., ].…”

Evidence of eddy-related deep ocean current variability in the North-East Tropical Pacific Ocean induced by remote gap winds

“…Our findings suggest that despite the significant modulation of dominant current directions driven by the bottom-reaching eddy, the current magnitude intensification was not strong enough to trigger local sediment resuspension in this region. A better insight of annual variability of ocean surface mesoscale activity in the CCZ and their effects on deep ocean current variability are of great help to mitigate the impact of the benthic ecosystem from future potential anomalous transport of momentum (Farneti et al, 2010;Hill et al, 2015), sediment (Washburn et al, 1993;Zhang et al, 2014;Aleynik et al, 2017), heat (Lyman and Johnson, 2015), oxygen (Stramma et al, 2014;Czeschel et al, 2018) and nutrients 60 (Müller-Karger and Fuentes-Yaco, 2000;Liang et al, 2009) into the ocean interior.…”