Spring–summer net community production, new production, particle export and related water column biogeochemical processes in the marginal sea ice zone of the Western Antarctic Peninsula 2012–2014

Abstract

New production (New P, the rate of net primary production (NPP) supported by exogenously supplied limiting nutrients) and net community production (NCP, gross primary production not consumed by community respiration) are closely related but mechanistically distinct processes. They set the carbon balance in the upper ocean and define an upper limit for export from the system. The relationships, relative magnitudes and variability of New P (from NO uptake), O : argon-based NCP and sinking particle export (based on the U :Th disequilibrium) are increasingly well documented but still not clearly understood. This is especially true in remote regions such as polar marginal ice zones. Here we present a 3-year dataset of simultaneous measurements made at approximately 50 stations along the Western Antarctic Peninsula (WAP) continental shelf in midsummer (January) 2012-2014. Net seasonal-scale changes in water column inventories (0-150 m) of nitrate and iodide were also estimated at the same stations. The average daily rates based on inventory changes exceeded the shorter-term rate measurements. A major uncertainty in the relative magnitude of the inventory estimates is specifying the start of the growing season following sea-ice retreat. New P and NCP(O) did not differ significantly. New P and NCP(O) were significantly greater than sinking particle export from thorium-234. We suggest this is a persistent and systematic imbalance and that other processes such as vertical mixing and advection of suspended particles are important export pathways.This article is part of the theme issue 'The marine system of the west Antarctic Peninsula: status and strategy for progress in a region of rapid change'.

Nitrogen and Isotope Flows Through the Costa Rica Dome Upwelling Ecosystem: The Crucial Mesozooplankton Role in Export Flux

“…Similarly, JGOFS studies in the equatorial Pacific and Arabian Sea have pointed to excess new production relative to export (Buesseler et al, , ; McCarthy et al, ; Sambrotto, ). In the western Antarctic Peninsula, twice weekly sampling has demonstrated that both nitrate uptake and net community production substantially exceed export from sediment trap and 238 U‐ 234 Th disequilibrium measurements when integrated over the phytoplankton growing season, and regional cruises have reported similar production‐export imbalances (Ducklow et al, ; Stukel et al, ). Similar imbalances have also been noted between the flux of sinking carbon out of the euphotic zone and the carbon demand of mesopelagic communities below (Burd et al, ).…”

A Modeling Study of the Marine Biogeochemistry, Plankton Dynamics, and Carbon Cycle on the Continental Shelf Off the West Antarctic Peninsula

“…The experiments that showed increased spatial correlation with the Palmer-LTER data also showed higher correlation with the coastal stations compared (Rothera Station and Palmer E). However, given that coastal sta- imbalance between estimated net community production (NCP) and sinking of particulate organic matter from the surface ocean has been observed [79] [19]. Although this imbalance is not unexpected given there are other fates and export pathways available for assimilated organic matter, such as remineralization and lateral transport, the magnitude of this imbalance at the WAP suggests that other pathways besides sinking could significantly affect the fate of the assimilated organic matter.…”

“…The composition of the WAP ecosystem, with important contribution of mesozooplankton grazers such as krill and salps, would suggest it is an efficient carbon pump. However, data collected at Palmer station during the phytoplankton growth season and from LTER cruises during the austral summer suggest a persistent and large imbalance between net community production (NCP) and particle sinking to the deep ocean [79] [19]. Although an imbalance between NCP and particle export is not unexpected given that assimilated organic matter can be remineralized or transported to a different region, the magnitude of this imbalance at the WAP suggests other mechanisms are at play.…”

The carbon: 234Thorium ratios of sinking particles in the California current ecosystem 2: Examination of a thorium sorption, desorption, and particle transport model

“…234 Th profiles are now regularly measured on survey cruises (e.g., Owens et al, 2015;van der Loeff et al, 2011), most of which do not have sampling plans that allow deployment of sediment traps for collecting particles for determination of the C: 234 Th ratio, which is necessary for converting 234 Th flux calculations into carbon flux estimates. Instead, such studies often rely on the C: 234 Th ratios of size-fractionated particles collected by in situ pump (often at only a subset of the stations sampled for total watercolumn 234 Th, e.g., Puigcorbé et al, 2017) or infer the C: 234 Th ratio from average regional estimates determined during other studies (e.g., Ducklow et al, 2018;Estapa et al, 2015). Such an approach is problematic because C: 234 Th ratios can vary substantially with depth, location, and time (Buesseler et al, 2006;Hung et al, 2004;Szlosek et al, 2009).…”