Cycling of organic carbon and biogenic silica in the Southern Ocean: Estimates of water-column and sedimentary fluxes on the Ross Sea continental shelf

Downward fluxes of particulate matter were investigated in the polynya of Terra Nova Bay (western Ross Sea) from February 1995 to December 1997. Biogenic silica made up the bulk of the sinking matter, reaching a maximum of 85% of the total flux in both the shallow and deep traps. Organic carbon accounted for 2.1 to 23.5% of the sample mass in the shallow trap and 2.8 to 7.2% in the deep trap. Biogenic silica and organic carbon peaks occurred in February–March over the three years and were always coupled in the top trap. Carbonate fluxes showed an uneven temporal trend, were low near the seafloor and contributed up to 69.8% of the material collected by the shallow trap. Vertical fluxes in the polynya showed large seasonal and interannual variability. Differences in primary productivity, ice cover dynamics and current energies accounted for the interannual changes in the flux of materials to the subsurface trap. Advection from sites a few hundred kilometres apart was the most likely reason for the decoupling between shallow and deep fluxes after October 1996. The seasonal pattern of downward fluxes was essentially linked to the seasonal cycle of primary production and spring–summer variations largely resulted from the composition of the phytoplankton assemblage in the overlying water column. The export of phototrophically produced materials to depth was low in late spring–early summer, at the time when Phaeocystis and small flagellates were the predominant autotrophs and the microbial food web prevailed over herbivorous feeding. Enhanced fluxes were linked to the predominance of large diatoms above the trap, in late summer. Temporal dynamics in this polynya were delayed by approximately one month as compared to the southernmost Ross Sea polynya, but showed the same temporal pattern: the time lag between production and accumulation of biogenic materials in the upper water column was a few weeks, while the delay in export from the surface layer relative to the maximum accumulation of biomass was approximately one month.

Download Full-text

Sediment characteristics at selected sites of the Ross Sea continental shelf: does the sedimentary record reflect water column fluxes?

Antarctic Science ◽

10.1017/s0954102003001123 ◽

2003 ◽

Vol 15 (1) ◽

pp. 133-139 ◽

Cited By ~ 9

Author(s):

M. FRIGNANI ◽

F. GIGLIO ◽

A. ACCORNERO ◽

L. LANGONE ◽

M. RAVAIOLI

Keyword(s):

Organic Carbon ◽

Water Column ◽

Biogenic Silica ◽

Ross Sea ◽

Sediment Traps ◽

Shelf Water ◽

Accumulation Rates ◽

Biogenic Components ◽

Mass Accumulation Rates ◽

Mass Accumulation

Flux data from moored sediment trap experiments and mass accumulation rates in sediments were obtained for three sites in the Ross Sea which are currently studied for the formation and transit of High Salinity Shelf Water and Ice Shelf Water. These two data sets were compared to obtain inferences on the coupling between water column processes and sedimentary records. The depth distribution of physical features and concentrations of organic carbon and biogenic silica in box cores and gravity cores were studied. Mass accumulation rates, established on the basis of two conventional 14C dates for each core, range between 7.64 and 19.46 g m−2 yr−1. Although these are productive areas, downward fluxes measured by sediment traps are low: 7.5–25.6, 2.4–17.9 and 0.5–0.9 g m−2 yr−1 for particles, biogenic silica and organic carbon, respectively. The concentrations of biogenic components in surficial sediments are correspondingly low. Simple mass balances were calculated assuming the conservative behaviour of the lithic fraction of sinking materials and sediment. Lateral advection of suspended particles is needed to balance the fluxes at the three sites. Furthermore, the model suggests that the preservation of biogenic components is lower than at other sites of the Ross Sea, probably due to the low accumulation rates that imply a high residence time of biogenic materials at the sediment-water interface.

Download Full-text

Biogenic-silica accumulation in the Ross Sea and the importance of Antarctic continental-shelf deposits in the marine silica budget

Geochimica et Cosmochimica Acta ◽

10.1016/0016-7037(86)90263-2 ◽

1986 ◽

Vol 50 (9) ◽

pp. 2099-2110 ◽

Cited By ~ 93

Author(s):

P.A Ledford-Hoffman ◽

D.J Demaster ◽

C.A Nittrouer

Keyword(s):

Continental Shelf ◽

Biogenic Silica ◽

Ross Sea ◽

Antarctic Continental Shelf ◽

Silica Budget

Download Full-text

Biogenic silica concentrations collected from CTD casts during RVIB Nathaniel B. Palmer cruise in the Ross Sea, Southern Ocean from 2017-2018

Biological and Chemical Oceanography Data Management Office ◽

10.1575/1912/bco-dmo.780191.1 ◽

2019 ◽

Author(s):

Giacomo DiTullio ◽

Peter Lee

Keyword(s):

Southern Ocean ◽

Biogenic Silica ◽

Ross Sea

Download Full-text

Vertical budgets for organic carbon and biogenic silica in the Pacific sector of the Southern Ocean, 1996–1998

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/s0967-0645(02)00005-x ◽

2002 ◽

Vol 49 (9-10) ◽

pp. 1645-1674 ◽

Cited By ~ 123

Author(s):

David M Nelson ◽

Robert F Anderson ◽

Richard T Barber ◽

Mark A Brzezinski ◽

Ken O Buesseler ◽

...

Keyword(s):

Organic Carbon ◽

Southern Ocean ◽

Biogenic Silica ◽

The Pacific

Download Full-text

Processes controlling the Si-isotopic composition in the Southern Ocean and application for paleoceanography

Biogeosciences Discussions ◽

10.5194/bgd-8-10155-2011 ◽

2011 ◽

Vol 8 (5) ◽

pp. 10155-10185 ◽

Cited By ~ 4

Author(s):

F. Fripiat ◽

A.-J. Cavagna ◽

F. Dehairs ◽

A. de Brauwere ◽

L. André ◽

...

Keyword(s):

Southern Ocean ◽

Isotopic Composition ◽

Water Column ◽

Mixed Layer ◽

Biogenic Silica ◽

Fractionation Factor ◽

Tropical Zone ◽

Weddell Gyre ◽

Elemental Cycling ◽

Si Isotopes

Abstract. Southern Ocean biogeochemical processes have an impact on global marine primary production and global elemental cycling, e.g. by likely controlling glacial-interglacial pCO2 variation. The natural silicon isotopic composition (δ30Si) of sedimentary biogenic silica has been used to reconstruct past Si-consumption:supply ratio in the surface waters. We present a new dataset in the Southern Ocean which includes for the first time summer δ30Si signatures of suspended biogenic silica (i) for the whole water column at three stations and (ii) in the mixed layer at seven stations from the sub-tropical zone up to the Weddell Gyre. In general, the biogenic silica isotopic composition at depth reflected a mixed layer origin and seemed not affected by any diagenetic effect in the water column, even if in the northern part of the Weddell Gyre an effect of biogenic silica dissolution cannot be ruled out. We develop a mechanistic understanding of the processes involved in the modern Si-isotopic balance, by implementing a mixed layer model. We observe that the accumulated biogenic silica (sensu Rayleigh) should satisfactorily describe the δ30Si composition of biogenic silica exported out of the mixed layer, within the limit of the current analytical precision on the δ30Si. The failures of previous models (Rayleigh and steady state) become apparent especially at the end of the productive period in the mixed layer, when biogenic silica production is low. This results from: (1) a higher biogenic silica dissolution:production ratio imposing a lower net fractionation factor and (2) a higher Si-supply:Si-uptake ratio supplying light Si-isotopes into the mixed layer. The latter effect is especially expressed when the summer mixed layer becomes strongly Si-depleted together with a large vertical silicic acid gradient.

Download Full-text