Grigorov1, I., A.
Kemp1 and S. Honjo2
1 Southampton Oceanography Center, Empress Dock, Southampton SO14 3ZH, UK; ivo_grigorov@hotmail.com, and 2 Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA
The Southern Ocean is a centerpiece in global biogeochemical cycles and ocean circulation. Recent drilling in the Atlantic Sector (ODP Leg 177, Shipboard Scientific Party, 1999) has recovered laminated diatom ooze sediments, spanning intermittently throughout the last 1.6 My (R. Pearce, unpubl.), which potentially record a seasonal surface water productivity signal (Grigorov et al., 2002).
An array of sediment traps, as part of the Antarctic Environment and Southern Ocean Process Study (AESOPS), deployed in the Indian Sector samples marine snow on its way from the surface waters to the sediment (Honjo et al. 2000). These are complimented by fluff layer and top 0.5 mm sediment surface samples.
The aim of this combined approach is two fold: (1) to establish the seasonal change in the diatom assemblage across the Polar Front and its alteration through the water column; (2) to test the hypothesis that laminated sediments from the Atlantic Sector contain an annual signal, and potentially act as a long-term sediment trap of seasonal flux.
Results to date show similarities between the inferred seasonality and sedimentation of assemblages from the sediment, and those sampled throughout the water column, due to the highly seasonal productivity pulse in the Southern Ocean. Although the mechanisms of formation of laminated sediments in the open ocean is not fully understood, they are thought to be associated with the productivity of the Polar Front. On a 100 000 yr scale, the stratigraphy of these deposits can track frontal migrations through time. In addition, time-series analysis of ~900 000 year old laminates show cyclicities identical to the Quasi-Bienniel Oscillation (QBO), El Niño-Southern Oscillation (ENSO) and the Antarctic Circumpolar Wave (ACW), all known to affect surface hydrography and primary production.
References:
Grigorov, I., R. Pearce & A. Kemp. 2002. Southern Ocean laminated diatom ooze: potential for paleo flux studies, ODP Leg 177, Site 1093. Deep-Sea Research II, 49, 3391
Honjo, S., R. François, S. Manganini, J. Dymond, R. Collier. 2000. Particle fluxes to the interior of the Southern Ocean in the Western Pacific sector along 170 W. Deep-Sea Research II, 47:3521-3548.
Shipboard Scientific Party. 1999. Leg 177 summary: Southern Ocean Palaeoceanography. In Gersonde, R., Hodell, D.A., Blum, P. et al. Proceedings of the Ocean Drilling Program, Initial Reports, vol. 177. College Station, TX (Ocean Drilling Program). 1-67.