Our geochemical studies in this region are in collaboration with colleagues at Qatar University. These include Jassem Al-Thani, Oguz Yigiterhan and  Ebrahim Al-Ansari.

A. Aeolian Dust

The Arabian Gulf is a very dusty place and this dust impacts biogeochemical processes. We studied the trace metal geochemistry of atmospheric dust on the Qatar Peninsula. About 33% of the total sample mass was CaCO3, reflecting the composition of surface rocks and soils in the source areas. Of the elements typically associated with anthropogenic activity, Ag, Ni, and Zn were most enriched, with enrichment factors (EF) of 182%, 233%, and 209%, respectively. Because river input is so small to the Arabian Gulf, the soluble fraction of this dust is a major source of nutrients (especially Fe) to surface seawater. See Yigiterhan et al. (2018) for the results.

B. Composition of Plankton

There have been few studies of trace metal biogeochemistry in coastal environments and marginal seas such as the Arabian Gulf. Data for the major and trace elemental composition of marine particulate matter are essential for our understanding of biogeochemical cycling in the ocean. We studied the elemental concentrations in small- and large-size fractions of net-tow particulate matter in coastal samples, in the Qatar Exclusive Economic Zone. We calculated the excess metal concentrations by correcting the bulk composition for inputs from atmospheric dust using aluminum (Al) as a lithogenic tracer and the metal/Al ratios for average Qatari dust. The concentrations of most elements (Al, Fe, Cr, Co, Mn, Ni, Pb, and Li) in net-tow plankton samples were mostly of lithogenic (dust) origin. See Yigiterhan et al. (2020) for the results.

C. Ocean Acidification

We have an on-going study of the ocean carbonate system in the Arabian Gulf. There is growing concern that coral reefs in the Exclusive Economic Zone (EEZ) of Qatar in the Arabian (Persian) Gulf have been severely impacted by ocean warming and ocean acidification. The goal of our studies is to assess the status of the ocean carbonate system with respect to present and future impacts by ocean acidification. There had been no previous studies of the complete carbonate system in this region. In our initial study we use distributions of DIC and TA to determine the relative importance of biological production and CaCO3 formation as sinks and sources of carbon and to determine pCO2 in surface seawater. We found that pCO2 in surface seawater averaged 458 ± 62 which was higher than the atmospheric value of 412 ppm. Hence, the Gulf was a source of CO2 to the atmosphere. pCO2 in seawater is controlled by TA relative to DIC as well as temperature and salinity.  See Izumi et al. (2022) for our results.

A.    San Francisco Bay

The eastern boundary upwelling system off the west coast of North America is more acidic than the open ocean. Upwelling of low O2, high NO3 and high pCO2 water, of equatorial origin,  from the California Undercurrent (CU) is a driving factor. We are analyzing a time series of data for temperature, salinity, oxygen and pCO2 from March 2013 to June 2015 at the Exploratorium Wired Pier in San Francisco Bay. pCO2 ranged from 550 to 1000 matm and was always higher than atmospheric values due to elevated DIC. This “natural” ocean acidification appears to be common on the US west coast. It dominates the “anthropogenic” component of ocean acidification in this region. This study is on-going.

B.    Mesocosm Experiments – Friday Harbor Laboratories

Large volume mesocosm studies were conducted at the UW Friday Harbor Laboratories to obtain information on how pelagic ecosystems respond to CO2 induced changes in seawater chemistry. The FHL location allowed experimentation on organisms, native to the northeastern Pacific, where a large “natural” ocean acidification signal has been detected. At this location typical nitrate and pCO2 concentrations are ~25 μmol kg-1 and ~650 μatm, respectively. Mesocosm test experiments were conducted in 2011, 2012 and 2013 to learn procedures and solve problems due to these unusual conditions. We are analyzing the data from 2013. The impacts of high CO2 on the biological community were small and in some cases contradictory. This may be because the biological community at Friday Harbor already lives in a high CO2 world and they may be at least partially adapted to high CO2 conditions. Based on the rates of change of O2, NO3 and chl, biological production may have been enhanced by the higher CO2. The grazer concentrations were also higher at high CO2. The bacterial populations were lower. There are several concentrations and rates that did not vary with CO2. This is also an important conclusion. This study is on-going.

Part of Murray’s research career started with focus on the surface chemistry and geochemical consequences of scavenging of trace elements by marine particles. Murray and his students were the first to conduct experimental and model studies to quantify the fundamental aquatic surface chemistry of iron and manganese oxides in seawater.(Murray (1974, 1975 a, b ; 1979; Murray and Dillard, 1979; Balistrieri and Murray, 1979, 1981; 1982 a,b)  . These oxides play an important geochemical role in trace element enrichment in the water column, sediments and manganese nodules. Based on these foundational studies they applied surface chemical concepts to predict scavenging of trace elements by marine particles ( Balistrieri and Murray, 1983, 1984, 1986, 1987; Honeyman et al., 1988; Jannasch et al., 1996). In Balistrieri et al (1981) they derived a model  to explain of trace metal enrichment as a function of water column depth at Bermuda and concluded that the surface chemistry of natural scavenging particles was controlled by organic coatings.

His lab produced the first profiles of chromium concentrations and oxidation states in the North Pacific Ocean (Cranston and Murray, 1978; 1980; Murray et al., 1983).

Murray then set up a lab to measure U-Th series isotopes to study the mechanism of scavenging and export of organic carbon in the ocean. Initial studies were in Puget Sound and the Black Sea (Wei and Murray., 1991, 1992, 1994). In 1992 he organized the US JGOFS Process Study of carbon cycling in the central equatorial Pacific (EqPac). There were follow up cruises in 1994 (FLUPAC), 1996 (Zonal Flux) and 2006 (EUCFe).  The physical, biological and chemical oceanography controlling the temporal and spatial variability of carbon cycling was synthesized in Science (Murray et al 1994). Murray’s specific research was to measure and model export production of carbon using a combination of approaches using 234Th/210Po/210Pb , drifting sediment traps and 15N new production rate measurements (Murray et al , 1989, 1996, 2005; Dunne et al., 1997, 1999, 2000; Aufdenkampe et al 2001, 2002a,b). It was significant that the new production was very low (e-ratio £ 0.1), in spite of the high NO3 concentrations, reflecting iron limitation (Loukos et al., 1997).  The significance was to show that though the equatorial undercurrent appears to be a source of Fe, the biological food-web is dominated by micro phytoplankton and zooplankton, thus carbon recycling is more important than export. In 2006 the EUCFe cruise clearly established that there the western source of iron from New Guinea, to the equatorial undercurrent (Slemons et al, 2009, 2010, 2012; Radic et al., 2011; Labatut et al., 2014).