Gulf of California 2012
March 1-11, 2012
Nearly the entire temperate to tropical eastern PacificOcean has strong gradients in both temperature and oxygen concentrations from the sea’s surface to its “bathyal zone” (the area of the ocean extending from depths of approximately 1,000 to 4,000 meters). Temperatures near 1,000 meters are typically around four to five degrees Celsius (39-41° F) with very low oxygen levels. These conditions are related to the high coastal productivity and the consumption of oxygen that occurs as bacteria break down the sinking organic debris.
In contrast, conditions in the deeper waters of the northwestern Gulf of California are quite different, due apparently to the downwelling of surface waters caused by shoreward Ekman transport. Seawater conditions at 1000 meters in the northwestern basins of the gulf are more typical of waters around 200 meters deep elsewhere, with warmer temperatures—around nine to 10° C (approximately 48-50° F)—and higher levels of oxygen.
The researchers on this leg of the expedition plan to deploy sensors on the seafloor in the Delfin and Salsipuedes basins of the northwestern gulf. From these sensors, scientists hope to obtain estimates of the seabed fluxes of nitrate. Researchers will also use the Benthic Respiration System to evaluate the metabolic rates of some of the larger denizens of the seafloor under normal, high-carbon dioxide, and high-oxygen conditions.
While conducting these seafloor respiration experiments, the researchers will also use ROV Doc Ricketts to perform surveys of the seafloor, and to collect samples using push cores and the suction sampler. The sediment cores brought up from the seafloor will serve two purposes. Researchers will analyze the faunal content of some of the sediment cores in order to discover which organisms make up the seafloor communities. Other sediment cores will be analyzed for their chemical content, providing an approximation of the flow of oxygen into or out of the sediment, an important factor for estimating the rate at which organic carbon is cycled back into the seawater.
The seafloor biology team will also conduct video transects with ROV Doc Ricketts to be used to document the larger inhabitants in the northwestern basins of the gulf. Once complete, scientists will perform similar studies in the waters off of La Paz in the southern part of the gulf, where seawater conditions are more typical of the eastern Pacific.