different temperature regimes, the similar, consistent differences 

 between the 5 '*0 values of water and tunicate cellulose for 

 tropical and temperate animals that lived at temperatures 

 differing by as much as 1 5°C ( DeNiro & Epstein, 1981) suggest 

 that, as in plants, there is no significant temperature effect on 

 oxygen isotope fractionation in tunicate cellulose. 



Material and Methods 



Stable Oxygen Isotope Composition-Seciwater and Tiinicates 

 Bottom seawater for stable oxygen isotope analyses were 

 subsampled in 20-ml vials, capped, sealed with Parafilm, and 

 returned to the laboratory. Oxygen isotope ratios of water 

 samples were determined by equilibrating 1 .0-ml water samples 

 with approximately 300 |i moles of carbon dioxide for 48 hours, 

 purifying the equilibrated carbon dioxide cryogenically, 

 analyzing the CO, mass spectrometrically, and using mass 

 balance considerations to calculate the original oxygen isotope 

 composition of the water (Epstein & Mayeda, 1953). 



Tunicates were collected from both a 0.1 -m- van Veen 

 grab (weighted with 32 kg of lead for enhanced penetration) 

 and otter trawl. Animals were sorted, keyed to species or 

 lowest taxon possible, and frozen in Whirl-pak bags. In the 

 laboratory, tunicates were freeze-dried and the body wall of 

 solitary animals dissected out for cellulose extraction. In the 

 case of colonial ascidians. a section of the outer region of the 

 animal was excised for extraction. Cellulose was extracted 

 using a sodium chlorite-acetic acid oxidation procedure (Wise, 

 1944), Oxygen isotope ratios of cellulose were determined by 

 pyrolyzing vacuum-dried and sealed samples in the presence of 

 HgCl, at 520° C for 5 hours to form CO, CO, and HCl. CO was 

 disproportionated to CO, and C by electrical discharge. HCl 

 was removed by reaction with isoquinoline (Epstein et ai. 

 1977). The CO, was then analyzed mass spectrometrically. 



Sediment Oxygen Uptake Rates 



Sediment samples for respiration experiments were 

 collected using a HAPS 0.0 1 33 m^ benthic corer or a box corer. 

 A shipboard core incubation technique for benthic metabolism 

 was used, following methods of Grebmeier and McRoy ( 1989), 

 which are based on experimental techniques of Pamatmat 

 (1971), Newrkla (1983), and Patching and Raine (1983). 

 Subsamples for core incubations were collected with 13-cm 

 diameter, 26-cm long acrylic cores ( 8-mni thick walls). Average 

 sediment depths were 10-15 cm, with the remainder of the core 

 barrel enclosing bottom water. Overlying bottom water was 

 carefully siphoned off and replaced with bottom water collected 

 with a Niskin bottle at the beginning of the experiment. The 

 cores were sealed with air-tight lids. Battery-operated stirrer 

 blades inside the core barrel mixed the water to reduce oxygen 

 gradient formation without disturbing the sedmients (Newrkla, 

 1983). Control laboratory experiments showed no disturbance 

 of sediment surfaces during stirring nor leakage of oxygen 

 through the container walls (Grebmeier & McRoy, 1989). 

 Cores were maintained in the dark at in situ bottom temperatures 

 for 8- 1 hours. This experimental duration has been determined 

 to be adequate for measurable depletion of oxygen (average 

 25%) in the chambers for similar sediments (Grebmeier & 



McRoy, 1989). Duplicate 60-ml water samples were collected 

 at the beginning of the experiment from the bottom water 

 Niskin bottle and at the end of the experiment from the 

 sediment cores for determination of dissolved oxygen content 

 by Winkler titration. After completion of the experiment, 

 sediment cores were washed through 1-mm stainless steel 

 screens. Animals were preserved in 10% seawater formalin, 

 buffered with hexamethyltetramine, stored in plastic Whirl- 

 pak bags, and saved for laboratory analy.ses (i.e., identification, 

 abundance counts, and biomass weights). 



Benthic Faiinal Abundance and Biomass 



Quantitative benthic samples were taken with the 0.1 m- 

 van Veen grab. Previous work in the Bering Sea (Feder et ai, 

 1973; Grebmeier, 1987) indicates that 4 grab samples per 

 station are adequate to account for natural statistical variability 

 at each station. Each sample was washed through 1-mm 

 stainless steel screens and animals subsequently preserved in 

 10% seawater formalin, buffered with hexamethyltetramine, 

 stored in plastic Whirl-pak bags, and saved for laboratory 

 analyses. Animals were keyed to family level, abundance was 

 recorded, then they were blotted dry and weighed to determine 

 wet-weight biomass. Wet-weight values were converted to 

 organic carbon biomass using previously verified conversion 

 values (Stoker, 1978; Grebmeier, 1987). The carbon conversions 

 enable comparison of biomass between stations by reducing 

 the influence of the calcium carbonate tests of mollusks and 

 echinoids on total biomass. Log-transformed abundance data 

 were analyzed using a numerical clustering program to group 

 stations according to faunal similarities (Feder et ai, 1985; 

 Grebmeier era/., 1989). 



Sediment Characteristics 



Surface sediment subsamples were taken from the van 

 Veen or Haps/box corer for total organic carbon and nitrogen 

 determinations at each station. Samples were dried at 105°C 

 overnight and homogenized with a mortar and pestle. One- 

 gram subsamples of surface sediment (0-1 cm) were acidified 

 with 2 ml of 1 N HCl and redried at 105°C overnight to obtain 

 carbonate-free sediments, and then rehomogenized. Carbon 

 and nitrogen contents were measured on a CHN analyzer. In 

 addition, sediment subcores were collected at representative 

 stations in each of the main basins, sectioned shipboard into 

 1-2 cm intervals, frozen, and returned to the laboratory. The 

 concentration of -'"Pb was measured by gamma-spectrometry 

 using low-background, high resolution, germanium detectors 

 equipped with a Nuclear Data Model 990 microprocessor 

 system programmed to record gamma spectra in 4,096 channels. 

 Samples were dried at 105°C overnight, homogenized, and 

 then packed in 90-cm' aluminum cans or 15-cm' plastic Petri 

 dishes, depending on the amount of material available. The 

 detectors were calibrated for the respective geometries with a 

 certified mixed standard and the calibration procedures are 

 described elsewhere (Olsen et ai, 1989). The low-energy 

 (46.5 keV) -'"Pb gamma-ray was analyzed using a planar 

 intrinsic-gennanium detector and correction for self-absorption 

 (Cutshall et al., 1983). This technique allows for direct 

 counting of radioactivity without leaching or radioactive 



245 



