Decadal Shifts in Biophysical Forcing of Arctic Marine Food Webs: Numerical Consequences

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Walsh, John J., Dieterle, Dwight A., Maslowski, Wieslaw, Whitledge, Terry E.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Digital Commons @ University of South Florida 2004
• Subjects: food webs; models; arctic; Life Sciences; Marine Biology; Beaufort Sea; Chukchi; Phytoplankton; Wrangel Island
• Online Access: https://digitalcommons.usf.edu/msc_facpub/164; https://doi.org/10.1029/2003JC001945; https://digitalcommons.usf.edu/context/msc_facpub/article/1163/viewcontent/Walsh_et_al_2004_Journal_of_Geophysical_Research_3A_Oceans__281978_2012_29.pdf

Fall case studies of threeâ€dimensional circulation, plankton, and benthos models explored the consequences of interannual changes in ice cover and water motion on carbon/nitrogen cycling by the end of September within the Chukchi/Beaufort Seas. The coupled model scenarios were those of reduced (greater) northward flow, colder (warmer) temperatures, and more (less) extensive ice cover over the preceding ∼60 days of August and September during the negative (positive), anticyclonic (cyclonic) phase of the Arctic Oscillation in 1980 (1989). On the inner Chukchi shelf, stronger flows in 1989 advected nitrate and silicate stocks of Pacific origin ∼130 km farther northwest toward Wrangel Island than in 1980. Yet an increase of the total net photosynthesis by the diatomâ€dominated phytoplankton community over both shelves in 1989 was mainly the result of less ice cover of the cyclonic period, with a concomittant increase of POC influxes of phytodetritus and fecal pellets to the sediments. In terms of present shelf export, the model's separate pools of ∼65 umol DOC kg−1 and 1 ug chl l−1, or ∼4 umol POC kg−1, at a depth of 60 m above the 2000â€m isobath of the Beaufort Sea in September 1989, matched the sum of ∼70 umol TOC kgâ€âˆ’1 sampled there by submarine in September 1997. Accordingly, most of the simulated Chukchi shelf was a weak sink of atmospheric CO2 in both September 1980 and 1989, reflecting a net fall export of particulate and dissolved debris. Within the cyclonic case of strong flows in 1989, a surface pCO2 of 248 uatm was also simulated in September at 155°W on the Beaufort shelf, where ∼250 uatm was measured there in September 2000. Here, farther away from the Pacific source of nutrients for enhanced photosynthesis, the model's estimate of surface sea water fugacity in a weaker flow regime was only 375 uatm of pCO2 at the same location in September 1980, when typically outgassing would have instead prevailed, despite increasing atmospheric pCO2 values, i.e., 356 to 362 uatm of pCO2 were ...