No abstract

Taphonomic processes in deep-water environments differ markedly from those in shallow waters. These differences are illustrated by the preservational style of a large cetacean skeleton lying at the bottom of the Santa Catalina Basin in 1,240 m of water. The degree of skeletal articulation contrasts with that documented in the shallow North Sea where gas-filled, buoyant carcasses disarticulated during flotation. Increased hydrostatic pressure at greater depth is presumed to have prevented the whale carcass from floating and promoted increased levels of preservation. We present a model that relates gas evolution during decay to carcass buoyancy with depth. Application of this model may ultimately allow the degree of skeletal articulation to be used as a rough index of paleobathymetry.

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The stable carbon isotope composition (613C) of particulate organic carbon (POC) was measured in 3 size fractions (POC,,,,I, POC,20,,r,,, POCcan,,,) during a phytoplankton spring bloom dominated by the diatom Skeletonerna costatum in Lindaspollene, a land-locked fjord in southern Norway. In addition to standard parameters for characterizing the phytoplankton bloom (chlorophyll, nutrient.and POC concentrations, and species composition), simultaneous measurements of F13c of dissolved inorganic carbon (DIC), total alkalinity and DIC concentration were obtained to determine temporal trends in dissolved carbon &oxide concentration and in carbon isotope fractionatlon (E,,) of the POC size fractions. The carbon isotope composition of the >20 pm size fraction, which was dominated by diatoms, was ca 2 2 , heavier than that of the c20 pm fraction, which was mainly composed of flagellates. 613C of both size fractions increased by about 3 %~ over the course of the bloom. A 5x0 increase in 613C-POC,,,,.I during the bloom resulted partly from a shift in the phytoplankton community from a flagellate-to a diatom-dominated one. Carbon isotope fractionation of all fractions decreased with declining C02(aq) concentration (14 to >6 pm01 I-'). A positive correlation between E, and [C02(aq)J in the diatom size fraction was obtained for the period of exponential growth. Deviation from this correlation occurred after the peak In cell density and chlorphyll a (chl a) concentration, when POC still continued to increase, and may be related to changing phytoplankton growth rates or to possible effects of nutnent (nitrate) limitation on %. Comparison of these results with those of previous field studies shows that, whlle an inverse relationship is consistently observed between E, and the ratio of instantaneous growth rate and CO2 concentration (pi/[C02(aq)]}, considerable scatter exists in this relationship. While thls scatter may have partly resulted from inconsistencies between the different studies in estimating phytoplankton growth rate, it could also reflect that factors other than growth rate and CO2 concentration significantly contribute to deterrninlng isotope fractionation by manne phytoplankton in the natural environment.

ABSTRACT. Mixed cultures of 4 polar diatoms regularly found in Antarctic pack ice were grown over 20 d In closed bottles at high light (200 to 250 pm01 photons m-' S-') and at 0°C in order to investigate growth physiology and biomass production under conditions simulating the sea ice habitat during summer. Species tested were: Chaetoceros cf. neogracile, Fragilariopsis c~~lindrus.