James W. Murray

Chemical Oceanography, UW School of Oceanography

Current Projects - Anoxic and Suboxic Environments

A Coastal Zone Color Scanner image of the Black Sea showing filaments that originate in the nearshore boundary current and extend into the interior of the basin.

Black Sea - Our recent interest in suboxic and anoxic environments started in 1988 when we organized the US-Turkish Black Sea Expedition. One of the most intriguing discoveries during that cruise was the suboxic zone (simultaneous low oxygen and low sulfide) of about 50m thickness separating the oxic surface water and the sulfide rich anoxic deep water (Murray et al., 1989; Codispoti et al., 1991; Murray et al., 1995). Poke here for representative oxygen and sulfide profiles from the western basin. These distributions suggest that the upward flux of sulfide is not being consumed by the downward flux of oxygen. The origin of this suboxic zone is uncertain but probably is related to oxidation-reduction reactions involving Mn, Fe, N and S species and the complex horizontal ventilation that occurs at these depths (Murray et al., 1991; Buesseler et al., 1991; Murray, 1995; Lee et al (submitted)). Many of the scientific results from that expedition were published in a special issue of Deep-Sea Research (Murray (Ed), 1991). Our own work included study of the physical regime (Murray et al., 1991a,b), nutrient distributions (Codispoti et al, 1991), Th234 (Wei and Murray, 1992), Th230 and Th232 (Huh et al., 1994) and Pb210 and Po210 (Wei and Murray, 1995).

We organized an international workshop titled "Physical and Ecological Data and Models of the Black Sea" in Tarabya, Istanbul from 11-13 October 1998. Sponsorship was provided by ONREUR, NSF, IOC, NATO and IMS-Erdemli. At this workshop we summarized the most recent data and models and made recommendations for future research. The workshop report is available here. The participants can also be seen on the deck of the Hotel Tarabya.

We presently have NSF funding to study the oxidation-reduction reactions involving N species in the suboxic zone. We are collaaborating with George Luther (Delaware) and Bradley Tebo (UCSD/Scripps) who are funded to study Mn, Fe and S cycling and Gernot Friederich (MBARI) who deploys a pump profiling system and measures carbonate system parameters. The field work includes international collaboration with colleagues at IMS-METU in Turkey (Temel Oguz, Sukru Besiktepe, Aysen Yilmaz and others) and MHI in Sevastopol, Ukraine (Konovalov, Ivanov).

The objectives of our group at UW include a through study of nitrogen cycling in the suboxic zone. The water column distributions suggest that there is a downward flux of NO3 that is consumed through reaction with Mn2+ and NH4+ to produce N2. Our study includes measurements of NO3, NH4, N2, PON and 15N-NO3, 15N-N2 , 15N-NH4 and 15N-PON. This will be the PhD Research of Amy Callahan (UW Chemistry Dept. graduate student). We also collaborate with Jim McCarthy (Harvard) and Aysen Yilmaz (IMS) who are studying 15N-NO3 new production in the euphotic zone.

Oxygen Minimum - Our recent research is also focussed on the intense oxygen minimum zone in the eastern tropical North Pacific off Mexico. Suboxic conditions exist in the water column of this region. Oxygen is low enough today in the 200m to 500m depth zone that denitrification is occurring. Denitrification at this site and two others (the eastern tropical South Pacific and the Arabian Sea) constitute one of the main sinks of nitrogen from the present day ocean. Our goal is to use the sedimentary record in long piston cores (collected in 1990) to determine if the oxygen minimum zone changed in intensity or depth during the last glacial maximum. The nitrogen isotope record suggests that less denitrification occurred during the last glacial period (Ganeshram et al., 1995). Recent UW chemistry graduate student, Tamara Nameroff, studied the present day and paleogeochemistry of the redox sensitive elements (Mn, Fe, U, V, Mo, Re) to obtain evidence to evaluate the hypothesis that the oxygen minimum was less intense in the past. A poster of these results was be presented at the 1995 SF AGU Meeting (Nameroff et al., 1995). The present day benthic fluxes for trace metals were determined using a bottom lander in collaboration with Dr. Allan Devol (UW). Nameroff completed her PhD thesis in 1996 and has two papers in progress. One is on the present day geochemistry and the other is on the paleo-distributions.

e-mail: jmurray@u.washington.edu

Updated 31 October 2001