Mesopelagic microplankton of the Arabian Sea
Document Type
Article
Date of Original Version
1-1-2003
Abstract
The Arabian Sea is notable for its dramatic monsoonal effects on euphotic zone biogeochemical processes and the large spatial extent of its mesopelagic oxygen minimum zone. As part of the US Joint Global Ocean Flux Study Arabian Sea project, we sampled microplankton (organisms 20-200 μm including diatoms, dinoflagellates, ciliates, sarcodines and nauplii) at five depths from 250 to 1000 or 1100 m at six stations during four seasonal cruises in 1995. Abundances of groups of organisms at discrete depths averaged 1-21-1 seasonally. Mean seasonal integrated biomass of the assemblage was 29 mg Cm-2 during the late Northeast Monsoon, 37 mg Cm-2 during the Spring Intermonsoon, 47 mg Cm-2 during the late Southwest Monsoon and 49 mg Cm-2 during the early Northeast Monsoon. Overall, protozoans dominated the mesopelagic microplankton assemblage. Integrated biomass peaked during the late SW Monsoon at two stations as expected if microplankton responded to surface productivity and mesopelagic organic carbon fluxes. At three stations, microplankton biomass peaked during the early NE Monsoon; this may reflect a continuing response to SW Monsoon productivity signals by these larger, slow-growing organisms. Protozooplankton abundance did not appear to be negatively affected by low (<0.1 ml dissolved O2 l-1) oxygen, whereas naupliar abundance and biomass were higher where oxygen concentration was higher. Total microplankton biomass was highest where oxygen concentrations and also mesozooplankton biomass were lowest, suggesting that predation also played a role in microplankton distributions. Calculations based on allometric relationships indicated that the mesopelagic heterotrophic microplankton assemblage could, on average, respire 9-38% of the particulate carbon flux that entered the system at 100 m and possibly 18-76% of the flux remaining at 250 m. Microplankton may therefore be significant carbon cyclers in the ocean's vast "twilight zone". © 2003 Elsevier Ltd. All rights reserved.
Publication Title, e.g., Journal
Deep-Sea Research Part I: Oceanographic Research Papers
Volume
50
Issue
10-11
Citation/Publisher Attribution
Gowing, Marcia M., David L. Garrison, Karen F. Wishner, and Celia Gelfman. "Mesopelagic microplankton of the Arabian Sea." Deep-Sea Research Part I: Oceanographic Research Papers 50, 10-11 (2003). doi: 10.1016/S0967-0637(03)00130-4.