Carbon fluxes forced by anticyclonic mesoscale eddies generated by islands at the subtropical NE Atlantic Ocean

Wang

et al. 2020

Front. Mar. Sci.

Mesoscale eddies frequently observed in the northern slope region of the South China Sea (SCS) significantly modulate the biological and biogeochemical behavior of organic carbon (OC). There have been few comparative studies on biological and biogeochemical processes in a pair of anticyclonic eddies (ACEs) and cyclonic eddies (CEs) in continental slope. In our research, an ACE-CE pair was observed in June 2015 on the northern slope of the SCS. The surface dissolved OC (DOC) was approximately 3 µmol L −1 higher in the ACE than that of the CE, and particulate OC (POC) was approximately 3.9 µmol L −1 higher in the CE than in the ACE. Along the transect across the ACE and CE, the concentrations of DOC and fluorescent dissolved organic matter (FDOM) were coincident with the downwelling and upwelling in the eddies. In the euphotic layer, the total OC (TOC) stock in the ACE was higher than that of the CE with a lower POC/TOC ratio. There was net consumption of both DOC and POC in the upper 120 m in the ACE; however, net POC production was observed within the CE. The results also indicated that the production of fresh OC was higher in the CE while carbon export was higher in ACE. The vertical export rates of DOC and POC at 120 m in the ACE were approximately 70.2 and 1.69 mmol C m −2 day −1 . Summarizing these measurements, the horizontal export of TOC across the slope to the SCS basin transported by dual eddies was estimated more than 22.1 × 10 9 g C. This estimate implies that mesoscale eddies can contribute significantly to carbon sequestration in the SCS.

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Hotspot of Organic Carbon Export Driven by Mesoscale Eddies in the Slope Region of the Northern South China Sea

Wang

et al. 2020

Front. Mar. Sci.

“…Very few factors substantially suppressed carbon export, except for the mesoscale anticyclonic eddy (Lasternas et al, 2012). Our SSHA data ( Figure 4G) exceeded 0.07 m at the beginning of July, directly suggesting the influence of the anticyclonic eddy (Roemmich and Gilson, 2001;Huang et al, 2010).…”

Section: Small Values In Summer Induced By Anticyclonic Eddymentioning

confidence: 69%

“…Based on the Bermuda Atlantic Time-series Study of the Sargasso Sea, Sweeney et al (2003) clearly showed that the 1994 spring bloom was suppressed by the passage of anticyclonic eddies with SSHA around 0.20 m. In the Norwegian Sea, warmcore eddies could delay the phytoplankton bloom by about 2 weeks (Hansen et al, 2010). Lasternas et al (2012) not only observed a considerable enhancement of dissolved organic carbon (DOC) concentration in the anticyclonic eddy center, but also diatom cell mortality rates of 60%. They proposed that the high mortality and cell lysis rates mainly resulted in the DOC increase, thereby reducing carbon export.…”

Section: Small Values In Summer Induced By Anticyclonic Eddymentioning

confidence: 99%

Deep Ocean Particle Flux in the Northern South China Sea: Variability on Intra-Seasonal to Seasonal Timescales

Tan

et al. 2020

Front. Earth Sci.

Based on a time-series sediment trap observation at a depth of 1,003-m in the northern South China Sea from 2014 to 2015, we used sinking particle flux combined with remote sensing-derived environmental data to infer the mechanisms of the biological carbon pump. Total particle flux, particulate organic carbon, CaCO 3 , and lithogenic (inorganic) fluxes peaked in winter and autumn but showed minima in summer, ranging from 59.7 to 413.2 mg m −2 d −1 , 2.1 to 18.2 mg m −2 d −1 , 32.9 to 197.9 mg m −2 d −1 , and 12.0 to 73.6 mg m −2 d −1 , respectively. Similarly, opal flux varied from 6.9 to 109.6 mg m −2 d −1 , with a prominent peak in winter and minimum in summer. However, a secondary maximum of opal in autumn was barely noticeable compared with other components. A deeper mixed-layer depth related to the northeast monsoon and surface cooling, overlapping with the effect of cyclonic eddies, is responsible for strong winter fluxes. When an anticyclonic eddy suppresses the subsurface nutrient supply, primary production and subsequent export flux in summer were reduced substantially. With respect to maximum lithogenic and CaCO 3 fluxes in autumn, a large aerosol optical depth suggests scavenging and mineral ballast effects as potential causes. This study highlights the importance of intra-seasonal physical processes (e.g., mesoscale eddies and aerosol deposition) to the deep particle flux in the South China Sea, as well as monsoonal transition.

“…In the northern hemisphere, most anticyclonic systems are oligotrophic, with nutrient-poor surface waters and restricted primary production. However, anticyclonic eddies (ACEs) are usually associated with relatively abundant microorganisms, an appreciable growth rate and DOC (dissolved organic carbon) accumulation (Bidigare et al, 2003;Ewart et al, 2008;Baltar et al, 2010), possibly triggered by downwelling in early-stage anticyclonic systems (Lasternas et al, 2012). DOC-rich surface waters and particulate organic carbon (POC) in ACEs were downwelled into deeper layers where extensive biogeochemical processing greatly affected its composition and the contributions of DOC to the oceanic carbon pump (Kolasinski et al, 2012;Lasternas et al, 2012).…”

Section: Introductionmentioning

confidence: 99%

Substantial Biogeochemical and Biomolecular Processing of Dissolved Organic Matter in an Anticyclonic Eddy in the Northern South China Sea Down to Bathypelagic Depths

Hertkorn

et al. 2022

Front. Mar. Sci.

Solid-phase extracted dissolved organic matter (SPE-DOM) was isolated from two depth profiles at the core and at the edge of an anticyclonic eddy (ACE) in the northern South China Sea. Non-target nuclear magnetic resonance (NMR) spectroscopy and Fourier transform ion cyclotron mass spectrometry (FTICR/MS) of SPE-DOM revealed a higher uniformity of DOM molecules within the ACE than at the edge of the ACE. Small-scale upwelling of external nutrients may have contributed to higher productivity and production of fresher DOM, with higher proportions of CHNO and CHNOS compounds and low molecular weight species at the edge of the eddy. Common SPE-DOM molecules of supposedly biological origin such as carbohydrates and olefins were most abundant in the chlorophyll maximum layer in both stations. An unusual suite of ~10 abundant and ~35 less abundant tert-butyl benzene derivatives with potential to act as endocrine disruptors within a marine food chain and ~two dozen ketones of putative bacterial origin was recognized at meso- and bathypelagic depths in single-digit micromolar concentrations, with a distinct maximum at 1000 m depth at the edge of ACE. Downwelling might bring temporary large volumes of productive marine waters into deep waters, with micromolar concentration of abundant, microbial food web-specific metabolites (e.g. 2,4-di-tert-butylphenol et al.). In our study, these eventually added up to one quarter of common background biogeochemical marine organic matter even at bathypelagic depths and beneath and are significant food and energy sources for marine biota. Mesoscale chemical heterogeneity of marine water columns might extend to larger depths than currently anticipated and may create activity hotspots influencing biota, processing of DOM, and cycling of nutrients and trace elements.