Anomalous conditions in the south‐eastern Bering Sea 1997: linkages among climate, weather, ocean, and Biology

Abstract

In 1997, the Bering Sea ecosystem, a productive, highlatitude marginal sea, demonstrated that it responds on very short time scales to atmospheric anomalies. That year, a combination of atmospheric mechanisms produced notable summer weather anomalies over the eastern Bering Sea. Calm winds, clear skies, and warm air temperatures resulted in a larger-than-normal transfer of heat to surface waters and the establishment of a shallow mixed layer. In spring, signi®cant new production occurred below the shallow pycnocline over the Middle Shelf, depleting the subpycnocline nutrient reservoir that normally exists during summer. Following the depletion of nitrate and silicate from the system, a sustained (³ 4 months) bloom of coccolithophores (Emiliania huxleyi) was observed ± a phenomenon not previously documented in this region. Summer Middle Shelf Domain copepod concentrations were higher for some species in 1997 than in the early 1980s. Warmer surface water and lack of wind mixing also changed the basic distribution of hydrographic regimes on the south-eastern shelf and altered the strength and position of fronts or transition zones where apex predators seek elevated food concentrations. The Inner Front was well inshore of its normal position, and adult euphausiids (the primary prey of short-tailed shearwaters, Puf®nus tenuirostris) were unavailable at, and shoreward of, the front in autumn. High shearwater mortality rates followed the period of low euphausiid availability. Some, but not all, of these anomalous conditions re-occurred in 1998. These observations are another demonstration that the structure and function of marine ecosystems are intimately tied to forcing from the atmosphere. Alteration of climatological forcing functions, expressed as weather, can be expected to have large impacts on this ecosystem and its natural resources.

Characteristics and variability of the inner front of the southeastern Bering Sea

“…By late August when storm winds did break down the stratification and set up the inner front farther seaward, no nutrients were available to mix upward. As a result of these factors, prolonged primary production did not occur at the inner front, which may have exacerbated the conditions that led to a die-off of short-tailed shearwaters (Puffinus tenuirostris) in August 1997 Napp and Hunt, 2001;Hunt et al, 2001). In 1998, ice was present only briefly during February, a time of weak wind mixing.…”

Recent climate variation in the Bering and Chukchi Seas and its linkages to large-scale circulation in the Pacific

“…The physical and numerical methods used in CAM3 are documented in Collins et al (2006) and the references therein. the warmest temperature ever observed before appeared in 1997, which is followed by rapid cooling until 1999 (Hunt et al 1999;Kruse 1998;Minobe 2002;Napp and Hunt 2001;Schumacher et al 2003;Stabeno et al 2001;Stockwell et al 2001). To identify any links between the Bering and Chukchi Seas and climate variability in the North Pacific, North Pacific (100°E-80°W, 20°-80°N) SSTA data were analyzed via CSEOF analysis.…”

“…The sea surface temperature (SST) in the Bering Sea increased up to 5-6°C above the average for August and September in 1997, and SST continued to be approximately 2°C higher than average through the summer of 1998. The biological conditions were also anomalous, including major cocolithophorid blooms, salmon returns far below predicted numbers, and the unusual presence of whales over the middle shelf (Hunt et al 1999;Kruse 1998;Minobe 2002;Napp and Hunt 2001;Schumacher et al 2003;Stabeno et al 2001;Stockwell et al 2001). It is likely that these changes in the Bering Sea are closely related to the state of the North Pacific climate system.…”

Remote Sensing of Sea Surface pCO2 in the Bering Sea in Summer Based on a Mechanistic Semi-Analytical Algorithm (MeSAA)

“…For example, coccolithophorid blooms have been found to frequently occur on the eastern shelf of the Bering Sea from August to October [84][85][86][87][88][89]; during the blooms, the cells release CO2 during calcification, consequently elevating the surface seawater pCO2 [88,89]. This process offsets the DIC consumption by photosynthesis.…”