Deep-St, Re,earth. ",'ol."~8. N,~ "~g. pp. I !-'~-[~43. [ti, OI OlUl'¢-Ol4~'t~[ $3 II~l. {I~:O Pnnted m ,(_,rc,tt Brtt..un ',~'SF [t~l PergamonPrc,,spie Sediment trap diatom assemblages from the northern Antarctic Peninsula region AMY LEVENTER* (Received 2 August 1981~; in revised fi~rm 15 October |990; accepted 23 October 1990) Abstract---Quantitative floral analyses were performed on 29 samples collected during ~24-h deployments of floating sediment traps. Traps were deployed at five sites in the northern Antarctic Peninsula region during December 1986 to March 1987. These analy,~cs and comparison to surface sediment data provide information concerning the influence of primary production, spore formation, post-bloom mass sedimentation, advection, and resuspension on the sinking and scdimcnted floral assemblage. At three of the five sites, absolute diatom flux decreased by more than an order of magnitude from January to February, the result of the sinking of bloom populations and subsequent decreased levels of primary productivity. These data indicate that at Ica,,t to 2~1 m, grazing and pelletization did not obscure the primary signal. Relatively low and unifornl diatom flux in Drake Passage was indicative of a deeply mixed surface layer in which peak levcls of biomass were rtot permitted to accumulate. Conver,~cly, uniformly high diatom fluxes at a linal site may have resulted from initi:dly high productivity fi~llowcd by a resu,~penxion event during February, perhaps the result of storm mixing that was documented by the increased relative percentage of benthic diatoms. The utility of diatoms as water mass tracer,, is demonstrated by the distribution of three floral as,~end'qagcs, both in the setlin~cnt traps and surface sediment samples. A di,~tiuct circunq~olar assemblage dominated by Nit=whia kerguch'nsis was observed in Drake I'assagc. A diatom assemblage conlpriscd of moderate to high abundances of Chaetoceros resting spores, Nitz~chia curta. :rod l'hah~ssioxira antarctica was broadly distributed through Bransticld Strait and l,ivingston Island contincnt:d shelf. Diatom flux in Gcrlachc Strait was domin:tted by resting spores of ('ha¢toceros. Northcastw:trd advection distributed these spores itlto Branslicld Strait where high (Tmetoccrox fluxes were observed at depth. (.'hcmic:d data suggest the possibility that spore formatit~n resulted from nutrient dcf~lction, hi neritic Antarctic waters, signilicant production and mass sinking of resting spores appears to be characteristic of the linal stages of an intense phytoplankton bloom. INTRODUCTION "l'tlE primary purpose of this study was to document quantitatively the floral composition of the settling diatom assemblage from five different sites in the northern region of the Antarctic Peninsula and the southern Drake Passage, based on analyses of sediment trap samples collected as part of the RACER (Research on Antarctic Coastal Ecosystem Ratcs) projcct (Tablc 1, Fig. 1). Southern Ocean phytoplankton are composed mainly of diatoms, with varying contributions of flagellates and other prymnesiophytes (i.e. Phaeo- cystis) (Hot.m-ttanseN et al., 1977; FrvxEt.L et al., 1984). Of these, diatoms have the grcatest potential to bc uscd as proxy indicators of palaeoproductivity, because their • Byrd Polar Research Center. The Ohio State University. Columbus. Otl 43210. U.S.A. 1127