Particulate Organic Carbon Composition in Temperature Fronts of the Northeastern Arabian Sea during Winter

Abstract

In order to understand the major sources of particulate organic carbon (POC) in the frontal zones and to examine their variability with space and time, a total of five temperature fronts of different ages was sampled in the northeastern Arabian Sea during winter. Compared to the nonfrontal regions, POC and chlorophyll‐a were higher within the coastal fronts, whereas chlorophyll‐a was lower within the open ocean front (T1). The variation of POC between coastal and open ocean fronts is attributed to the combined influence of variable vertical mixing, heterotrophic transformation and age of the front. Relatively depleted δ13CPOC and δ15NPN were observed within the fronts, suggesting that POC pool is contributed by in situ production supported by upwelling of nutrient‐rich water and zooplankton biomass. Elemental C:N ratios, POC:Chl‐a, δ13CPOC, and δ15NPN suggest that POC is mainly contributed from primary producers and heterotrophs in the study region. However, relative contributions from these two sources vary spatially from coastal to open ocean and with the age of the front. Stable Isotope Analysis in R (SIAR) model revealed that zooplankton biomass largely contributed to POC in the open ocean (60–80%) than phytoplankton (20–40%) and nearly equal contribution was observed in the coastal fronts (50–60% and 40–50%, respectively). This study, thus, demonstrates that dominant heterotrophy and autotrophy in the open ocean and coastal fronts and it is consistent with their biomasses. Predominant heterotrophy in the open ocean is attributed to deeper mixed layer resulting in upwelling of bacteria‐rich and phytoplankton‐poor water to surface leading to existence of microbial loop.

Effects of Typhoon Mujigae on the Biogeochemistry and Ecology of a Semi‐Enclosed Bay in the Northern South China Sea

“…Positive AOU values and unsaturated DO values (Figures 4e and 4g; Table 1) were found in most cases, owing to organic matter decomposition (Fu et al., 2020; Yuan et al., 2011). The strong positive linear correlation between PN and POC ( p < 0.001, R 2 = 0.89) indicates that POC and PN share similar biogeochemical processes during the typhoon periods, and their decoupling with Chl a (both p > 0.05) further suggests the decomposition of organic matter (Krishna et al., 2018).…”

Open-Ocean Minima in δ13C Values of Particulate Organic Carbon in the Lower Euphotic Zone

“…Non-tabulated data points (Saino, 1992) and coordinates locations (Trull et al, 2008) were extracted using a built-in MATLAB function (ginput); data are compiled in Supplementary Table S2. We excluded some published studies from our numerical analysis due to a scarcity of depths sampled in the upper water column or due to likelihood of terrigenous inputs, low-oxygen metabolisms, or experimental manipulations (Williams and Gordon, 1970;Eadie and Jeffrey, 1973;Druffel et al, 1996;Benner et al, 1997;Trull and Armand, 2001;Hernes and Benner, 2006;Close et al, 2014;Krishna et al, 2018;Liu et al, 2018). We also did not include data from the Arctic region due to the prevalence of terrigenous or advected POC in these areas (e.g., Griffith et al, 2012;Xiang and Lam, 2020).…”

Isotopic analysis of otolith carbonates using laser heating: A fast method for obtaining high‐resolution climate signal

“…The δ 13 C values of the particulate organic carbon and phytoplankton of this location average to ~ −25‰ 46 . The mature Arius sp.…”

“…The δ 13 C values of the particulate organic carbon and phytoplankton of this location average to $ À25‰. 46 The mature Arius sp. catfish feeds on small marine invertebrates like molluscs and secondary consumers like smaller fish.…”