Oceanography

Physical and Chemical Oceanography

Lisa Eisner

Objectives – (1) Assess circulation and water masses on the eastern Chukchi Sea shelf and (2) assess horizontal and vertical variability in nutrient and Chlorophyll a concentrations over the shelf.

While numerous water column profiles and other oceanographic measurements have been obtained on the Chukchi Sea shelf during the open-water season, this survey will provide one of the first comprehensive and near-synoptic oceanographic surveys covering the shelf from the Bering Strait to the shelf edge. The project will collect vertical profiles of conductivity, temperature, depth (CTD), light transmission, chlorophyll-a fluorescence, dissolved oxygen, pH, photosynthetic available radiation (PAR), and nitrate concentrations, as well as surface along-track measurements of temperature and salinity. These data will be used to characterize the physical environment (water masses and circulation, availability of light and nutrients) and are anticipated to be used for supporting and validating physical oceanographic models such as the model being developed by Enrique Curchitser (Rutgers) under a separate BOEM cooperative agreement. The University of Washington, Marine Chemistry Laboratory will be contracted to analyze nitrate, nitrite, ammonium, phosphate, and silicate following standard protocols (UNESCO 1994). Chlorophyll-a samples will be analyzed at the Alaska Fisheries Science Center (AFSC) following protocols developed by Parsons et al. (1984).

2013 Field Update

In the Chukchi Sea, CTD casts were conducted at 104 stations. Discrete water samples were collected with Niskin bottles during CTD casts at 58 of these stations. In the Northeast Bering Sea, CTD casts and water samples were collected at 45 stations. Preliminary observations for 2013 in the NE Chukchi Sea indicate that temperature decreased and salinity increased from inshore to offshore, similar to 2012. Near the ice edge, the freshwater sill was prominent with very cold temperatures (-1.5 °C) below the shallow thermocline or freshwater sill. In Barrow Canyon there was a freshwater sill on top of Shelf/Pacific water on top of Atlantic water from the north. This was the location where Age1+ Arctic Cod were caught.

Figure 1. Preliminary analysis suggests the 2013 mean surface temperature was 7.7 ⁰C, close to the 12 year average.

Surface (5m) seawater temperature anomalies were evaluated for the northeastern Bering Sea (NBS) (60 to 65.5 ⁰N) over bathymetry ~20-60 m depth from 2002 to 2013. Preliminary analysis suggests the 2013 mean surface temperature was 7.7 ⁰C, close to the 12 year average (Figure 1). 2013 CTD temperature data in addition to other parameters for the eastern Chukchi Sea are currently being processed, but will be available soon.

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