Seasonal distribution of dissolved inorganic carbon and net community production on the Bering Sea shelf

Abstract

Abstract. In order to assess the current state of net community production (NCP) in the southeastern Bering Sea, we measured the spatio-temporal distribution and controls on dissolved inorganic carbon (DIC) concentrations in spring and summer of 2008 across six shelf domains defined by differing biogeochemical characteristics. DIC concentrations were tightly coupled to salinity in spring and ranged from ∼1900 µmoles kg −1 over the inner shelf to ∼2400 µmoles kg −1 in the deeper waters of the Bering Sea. In summer, DIC concentrations were lower due to dilution from sea ice melt, terrestrial inputs, and primary production. Concentrations were found to be as low ∼1800 µmoles kg −1 over the inner shelf. We found that DIC concentrations were drawn down 30-150 µmoles kg −1 in the upper 30 m of the water column due to primary production and calcium carbonate formation between the spring and summer occupations. Using the seasonal drawdown of DIC, estimated rates of NCP on the inner, middle, and outer shelf averaged 28 ± 9 mmoles C m −2 d −1 . However, higher rates of NCP (40-47 mmoles C m −2 d −1 ) were observed in the "Green Belt" where the greatest confluence of nutrient-rich basin water and iron-rich shelf water occurs. We estimated that in 2008, total NCP across the shelf was on the order of ∼96 Tg C yr −1 . Due to the paucity of consistent, comparable productivity data, it is impossible at this time to quantify whether the system is becoming more or less productive. However, as changing climate continues to modify the character of the Bering Sea, we have shown that NCP can be an important indicator of how the ecosystem is functioning.

Circulation on the central Bering Sea shelf, July 2008 to July 2010

“…These various lines of evidence have important implications for biological production, since they suggest that the rich nutrient load in the Gulf of Anadyr can be brought onto the central shelf region at least as far south as Nunivak Island under sustained southeastward flow (e.g., a monthlong mean speed of 10 cm s −1 ). Indeed, this nutrient pathway may at least in part explain the recent observation of elevated net community production over the central shelf [ Mathis et al , 2010].…”

“…Our primary goal here is to gain a better mechanistic understanding of the central shelf flow and its relation to the varying wind and thermohaline fields. Our results bear on numerous eco‐ and climate system issues, including aspects of salmon migratory behavior [ Mundy and Evenson , 2011], advection of passively drifting larvae [ Wespestad et al , 2000; Wilderbuer et al , 2002; Orensanz et al , 2004], nutrient replenishment and net production over the Bering shelf [ Sambrotto et al , 1986; Whitledge et al , 1986; Mathis et al , 2010], and heat, nutrient, and fresh water fluxes northward into the Arctic Ocean [ Aagaard and Carmack , 1989; Woodgate et al , 2010].…”

Absorption and fluorescence properties of chromophoric dissolved organic matter of the eastern Bering Sea in the summer with special reference to the influence of a cold pool

“…Water masses in the eastern Bering Sea during the summer could be divided into three main groups with salinity < 31.3 for ice melt and river water, 31.3-33 for the Bering shelf water, and 33-35 for the deep Bering Sea (DBS) ( Fig. 2a and b; Mathis et al, 2010). A pronounced frontal zone divides the shelf waters from the deep basin ( Fig.…”

Annual sea‐air CO2 fluxes in the Bering Sea: Insights from new autumn and winter observations of a seasonally ice‐covered continental shelf

“…While mixing processes are likely minor contributors to changes in buffering capacity, lateral and vertical advection can change nΔ p CO 2 (sw) by increasing or decreasing CO 2 concentrations in surface waters. Insofar as these changes are related to biological modification, as when respiration‐impacted waters are mixed into the surface layer [ Mathis et al ., ; Cross et al ., ], this does not represent a significant source of error to our biological term. The impact of lateral advection of new water masses is also minimal.…”

“…Few previous observations later in the year than September exist, and the biogeochemical processes occurring during autumn and winter (“late season”; i.e., October to March) are not well understood. Earlier work has shown that respiration processes cause CO 2 accumulation in bottom waters over the shelf during the preceding summer, particularly in regions corresponding to high primary production levels in the overlying surface waters [e.g., Mathis et al ., ; Cross et al ., ; Mathis et al ., ]. We observed here that biogeochemical processes substantially modified surface waters in autumn and winter.…”