Carbon Export in the Coastal Upwelling System of Monterey Bay
ID：609
Invited Oral Presentation
2027-01-14 08:45 （China Standard Time）
Session：Session 49 - Biological Carbon Pump: New Insights from Field Observations and Model Constraints
Abstract
Continental ocean margins supply as much as 50% of the carbon transferred by the biological pump to the deep ocean (Jahnke, 2010) however there have been few studies of new and export production in these regions. Eastern boundary upwelling areas, like the California current, make the largest contribution to basin scale fluxes. In order to quantify the magnitude and seasonal variability of carbon cycling in a coastal upwelling region we conducted a detailed study in Monterey Bay, California. Nine cruises were conducted over a 14-month period from June, 1990 to August 1991 and we measured primary (14C) and new (15N) production, POC, PON and POP in the water column and in drifting sediment traps and dissolved, particulate, total and sediment trap 234Th. Primary production and new production were highest in the spring (April – June) and lowest in the winter (November – February) and varied from 39 to 165 mmol C m-2 d-1 and 2 to 24 mmol N m-2 d-1, respectively. Export production was measured using 234Th calibrated drifting sediment traps (Murray et al., 1996). The C / 234Th ratios in suspended particulate matter in the euphotic zone varied systematically with time and depth and ranged from 15 to 140 μmol/dpm. The highest values were in spring and at the surface. The C / 234Th ratios in sediment traps had the same temporal and spatial variability but were lower and ranged from 7 to 27 μmol/dpm. 234Th and POC were correlated in trap samples supporting the argument that 234Th is a tracer for the POC flux and can be used as a correction factor for trap bias. As found previously, the PIT design traps tended to over collect 234Th (and thus carbon) relative to the calculated 234Th flux by up to 5-fold. The largest over trapping occurred in the spring. The export production of POC was calculated from the 234Th deficiency in the water column and the C/234Th ratio in traps at the base of the euphotic zone (~60m). The POC export production at 60m varied from 7 to 39 mmol C m-2 d-1. f-ratios (NO3 / NO3 + NH4) from 15N varied from 0.21 to 0.74 and e-ratios (C flux / PP) varied from 0.05 to 0.68. The e-ratio was usually less than the f-ratio. These results suggest a seasonal two-state system that varies from a coastal state in the summer with high primary, new and export production and high e- and f-ratios to an open ocean-like state in winter with lower primary, new and export production and lower e- and f-ratios. A similar two-state system was proposed by Bruland et al. (2001) based on iron-replete versus iron-deficient conditions. The Total POC export from the California Current (area = 9 x 1011 m2) assuming an average POC export = 21.9 mmol C m-2 d-1 (= 95.9 gC m-2 y-1) is 86 x 1012 gC y-1, which is a significant fraction of the carbon export from the North Pacific Eastern Boundary Current.
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Jan 30
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