Early winter barium excess in the southern Indian Ocean as an annual remineralisation proxy (GEOTRACES GIPr07 cruise)

[摘要] The Southern Ocean (SO) is of global importance to the carboncycle, and processes such as mesopelagic remineralisation that impact theefficiency of the biological carbon pump in this region need to be betterconstrained. During this study early austral winter barium excess(Ba xs ) concentrations were measured for the first time, along30 ∘  E in the southern Indian Ocean. Winter Ba xs concentrations of 59 to 684 pmol L −1 were comparable to those observedthroughout other seasons. The expected decline of the mesopelagic Ba xs signal to background values during winter was not observed, supporting thehypothesis that this remineralisation proxy likely has a longer timescalethan previously reported. A compilation of available SO mesopelagicBa xs data, including data from this study, shows an accumulation rateof ∼0.9   µ mol m −2  d −1 from September to Julythat correlates with temporally integrated remotely sensed primaryproductivity (PP) throughout the SO from data spanning ∼20  years, advocating for a possible annual timescale of this proxy. Thepercentage of mesopelagic particulate organic carbon (POC) remineralisationas calculated from estimated POC remineralisation fluxes over integratedremotely sensed PP was ∼2 -fold higher south of the polarfront (19  ±  15 %, n =39 ) than north of the polar front (10  ±  10 %, n =29 ), revealing the higher surface carbon exportefficiency further south. By linking integrated remotely sensed PP tomesopelagic Ba xs stock, we could obtain better estimates of carbonexport and remineralisation signals within the SO on annual and basinscales.

[学科分类] 大气科学