Sargasso Sea phosphorus biogeochemistry: an important role for dissolved organic phosphorus (DOP)

Abstract

Abstract. Inorganic phosphorus (SRP) concentrations in the subtropical North Atlantic are some of the lowest in the global ocean and have been hypothesized to constrain primary production. Based upon data from several transect cruises in this region, it has been hypothesized that dissolved organic phosphorus (DOP) supports a significant fraction of primary production. In this study, a time-series of phosphorus biogeochemistry is presented for the Bermuda Atlantic Time-series Study site, including rates of phosphorus export. Most parameters have a seasonal pattern, although year-over-year variability in the seasonal pattern is substantial, likely due to differences in external forcing. Suspended particulate phosphorus exhibits a seasonal maximum during the spring bloom, despite the absence of a seasonal peak in SRP. However, DOP concentrations are at an annual maximum prior to the winter/spring bloom and decline over the course of the spring bloom while whole community alkaline phosphatase activities are highest. As a result of DOP bioavailability, the growth of particles during the spring bloom occurs in Redfield proportions, though particles exported from the euphotic zone show rapid and significant remineralization of phosphorus within the first 50 m below the euphotic zone. Based upon DOP data from transect cruises in this region, the southward cross gyral flux of DOP is estimated to support ~32% of annual primary production and ~100% of phosphorus export. These estimates are consistent with other research in the subtropical North Atlantic and reinforce the hypothesis that while the subtropics may be phosphorus stressed (a physiological response to low inorganic phosphorus), utilization of the DOP pool allows production and accumulation of microbial biomass at Redfield proportions.

Dissolved organic phosphorus production and decomposition during open ocean diatom blooms in the subarctic Pacific

“…Despite its importance, DOP dynamics have been understudied. Seasonal variations in DOP concentration have been reported in coastal regions (Monaghan and Ruttenberg, 1999;Van Der Zee and Chou, 2005) and open subtropical regions (Karl and Tien, 1997;Lomas et al, 2010). We also reported multiyear DOP dynamics in Funka Bay, Hokkaido, Japan (Yoshimura and Kudo, 2011).…”

“…DOP dynamics have not been fully examined in the relatively productive subarctic regions compared with the comprehensive studies in subtropical oligotrophic regions such as stations ALOHA (Karl and Tien, 1997) and BATS (Lomas et al, 2010). In the Oyashio region, a western boundary current of the subarctic circulation in the North Pacific, phytoplankton growth is regulated by nitrate, silicic acid, and iron while a significant amount of soluble reactive P (SRP) remains throughout the year (Nakayama et al, 2010;Nishioka et al, 2007;Saito et al, 2002).…”

Dynamics of Dissolved Organic Phosphorus

“…Based on model calculations, the input of DOP (locally equivalent to "new" P) is 12 mmol P m −2 year −1 , which is sufficient to support approximately 50% of P lost in sinking particulate matter (Roussenov et al, 2006). In a separate study, Lomas et al (2010) supported this hypothetical flux of DOP into the North Atlantic subtropical gyre via transport by subtropical mode water. Based on a comprehensive 5-year data set collected at the Bermuda Atlantic Time-series Site (BATS) that included multiple P pools and their dynamics, the authors concluded that imported DOP supports approximately 25% of annual primary production and essentially all of the P exported as sinking particles.…”

A three-dimensional model of Lake Superior with ice and biogeochemistry

“…Phosphorus appears to limit summer production, though iron may also play a role (Sterner et al, 2004). Recent measurements of dissolved organic phosphorus (DOP) show the presence of a seasonally highly dynamic pool , suggesting the possibility that DOP may be fueling production in Lake Superior as in the Sargasso Sea (Lomas et al, 2010). Nitrate limits production in many parts of the world ocean, but it is in constant excess in Lake Superior.…”