Direct Mixing Observations in the Denmark Strait Overflow Area
The Denmark Strait area is one of the key locations for the global thermohaline circulation, acting as the main chocking point for dense water and its ability to communicate with the world’s oceans. I have been offered to participate in the RRS Discovery cruise to the overflow area in September-October 2006 together with European colleagues Bert Rudels and Detlef Quadfasel. The cruise aims at obtaining detailed direct (and indirect) mixing observations in the Denmark Strait overflow plume and to investigate the upstream sources of the overflow.Moreover, we will also serve and cycle various moorings that are deployed in this area. The overall goal is to better understand how these dense waters communicate and contribute to the global thermohaline circulation, and how ongoing and future changes in these overflows may affect our oceans and global climate using new state-of-the-art instruments and technology.
Exploring the Feasibility of Glider-Based Transport, Stratification and Ecology Measurements on the New England Shelf Between MVCO and Line W
David Fratantoni, Heidi Sosik, John Trowbridge
The continental shelf from Nova Scotia to CapeHatteras is one of the most productive ecosystems on Earth. This high productivity is based on a complex set of chemical and biological interactions that begin with nutrients and plankton, and which are critically linked to the physics of water motion and mixing. Because human populations along this coastline continue to increase, the demand for coastal resources (e.g., fisheries, properties, and recreation areas) is growing at the same time that human-induced disturbances (e.g., nutrient loading, contaminant inputs, and introduced species) are increasing. Improved scientific understanding is sorely needed as the basis for responsible stewardship of this system in the face of societal concerns and as yet unpredictable consequences of climate change1.
Previous work, both moored and ship-based, has indicated the need for both highly-resolved spatial measurements (to describe features on scales of 1-10 km) and a sustained at-sea presence (to capture episodic events and facilitate robust statistical inferences). Ship-based measurements on the continental shelf are generally expensive and weather dependent. Moored observations generally lack spatial resolution. Autonomous vehicles, when used appropriately relative to their inherent capabilities, can provide sustained, low-cost, and robust measurements of key physical and biological variables. A question of particular relevance at the present moment is: “How can these novel assets be most effectively employed in coastal observing systems?”
We propose to study, from both scientific and engineering perspectives, the feasibility of using autonomous gliders for regular collection of physical and bio-optical properties along a 200 km transect spanning the continental shelf and connecting the Martha’s Vineyard Coastal Observatory (MVCO) with the Line W moored climate array. The proposed work constitutes an important step in the development of an integrated and sustainable regional observing system capable of resolving physical and biological variability on timescales from days to decades.
This proposal requests support for the salary, shiptime, and expendables required to complete and analyze a series of feasibility experiments totaling more than 200 glider-days at sea.
Exploring Non-Traditional Stable Isotope Systematics in Back-Arc Hydrothermal Systems
Variations in the isotopic ratios of light elements such as H, C, N, O and S have been widely studied over the last five decades and provided the foundation for the field of Stable Isotope Geochemistry. These traditional stable isotope systems have been applied to a range of problems such as planetary geology, the origin and evolution of life, climate change, and water-rock interactions. However, much less attention has been paid to the stable isotope variations of heavier elements, such as Fe, Cu, Zn, Cr or Mo mainly due to analytical challenges. With the advent of multi-collector inductively-coupled plasma mass spectrometry (MC-ICPMS), large numbers of non-traditional stable isotopes are now accessible to stable isotope studies that should lead to unprecedented discoveries in biogeochemical cycles.
Past studies have highlighted the importance of subseafloor environments in controlling the diversity of seafloor hydrothermal vents. It is also well known that these environments harbor a diverse and unique biological community capable of using dissolved chemical species and minerals for energy metabolism. However, the mechanisms and extent of subseafloor metal precipitation, remobilization and bacterial cycling are still poorly constrained and new approaches are required.
Recently, I started the investigation of non-traditional isotope systematics of hydrothermal fields at East Pacific Rise and Mid-Atlantic Ridge and developed conceptual models for using Iron, Copper, Selenium and Germanium isotopes as new tracers of subsurface environments. Here, I request support to participate to an up-coming cruise on the EasternManusBasin (Aug. 2006) to perform preliminary research on nontraditional stable isotope systematics of hydrothermal vents in back-arc environments characterized by contrasted fluid chemistry and source rock composition relative to midoceanic ridge systems. Having the possibility to join this cruise on the R/V Melville with ROV Jason II (W. Bach and M. Tivey, co-chief scientists) would complement ideally my on-going work on East Pacific Rise at 9-10°N and will permit to further constraint the fundamental parameters controlling isotope fractionation, including the temperature and pH of the hydrothermal fluid, phase separation process, the presence of magmatic fluids, the mineralogy of hydrothermal precipitates, and, potentially, the role of biological activity.
One of the best means of observing changes in time, in the ocean, is through the use of moorings. These consist of a line of instruments, anchored to the seafloor and rising towards the surface that is deployed from a ship and left in the water until recovery (typically months or years later). Moorings, however, have one serious limitation: it is very difficult to obtain near surface measurements. This is a practical limitation dictated by the threat to moorings posed by ship traffic, fishing gear, ice in polar regions and, in general, wear and tear from surface waves.
Recently, engineers at WHOI have found a solution to this problem: the winched profiler. It consists of a winch, mounted on the top of the mooring (at 50m below the surface, for example), which periodically allows a sensor carrying parcel to rise to the seasurface. Once at the surface the parcel is pulled back and safely stowed until the next measurement. The profiler is thus a means of obtaining measurements from the surface layer without leaving any permanent part of the mooring there. A first version of this instrument, fitted for the polar regions, was recently deployed and recovered after one year by Straneo in HudsonStrait. The instrument performed well and proved that this is a powerful, new tool for moored ocean observing platforms.
Given this first successful mission of the instrument in its most basic form, Straneo is now planning to use the profiler in a continued, and more thorough, monitoring of the freshwater flow through Hudson Strait, one of the major gateways for the Arctic/Atlantic exchange and a strategically important climate region. For this task, however, the profiler must be modified to increase its reliability as well as its sensor load. Specifically, funds are requested to: 1) guarantee that the data are saved even if the parcel is lost, 2) add a new temperature/salinity sensor that can be easily combined with biological and chemical sensors, 3) add a fluorometer to the sensor load which would allow to identify the sources of freshwater. While motivated by a specific project, these modifications are generally necessary to ensure the adaptability of the instrument to a wide range of multidisciplinary oceanographic applications.
Diversity and Quantity of Metabolically Active Microbial Communities within the Stratified Black Sea: Do these organisms form genetic archives for paleoclimate reconstructions?
Post-glacial climate-induced hydrological changes from freshwater lake to the present day stratified and mainly anaerobic saline Black Sea must have had a great impact on the diversity and quantity of ancient phyto- and picoplankton (bacteria and archaea) ice versa, from the knowledge about the past species composition, important climate-induced variations of the past water column environment can be deduced such as surface water temperature, salinity, presence or absence of oxygen etc. In return, changes in hydrological parameters do affect our climate. Recently, I received a grant from NSF in order to study chemical fossils in Holocene sediment record from the Black Sea which form an archive of the ancient species composition. The novelty of the grant is to study the ancient species composition also based on fossil DNA sequences which are promising ultimate “biomarkers” because they can provide information at the unprecedented species level for much more accurate paleoecological and paleoclimate
reconstructions. A 6-day-long cruise is funded by NSF in order to collect sediment cores for the ancient DNA archive work but it would be essential to be able to collect particulate organic matter (POM) from the present-day water column in order to compare the paleoecological data (NSF grant) with the modern species diversity.
I, therefore, request funding via the Access to the Sea program to extend the Black Sea cruise for 3 days in order to collect POM by filtration from 20 positions in the photic zone at two sites in the Black Sea where also the sediment coring will take place. The photic zone (upper ~130 m) includes an interesting gradient of micro organisms that are restricted to thrive at certain regions of the oxygenated, and year-round stable suboxic and sulfidic layers. So far, a highly resolved analysis of the diversity and quantity of active microbiota in the Black Sea’s photic zone is lacking and a comparison of these species in the fossil record will reveal to what extent the modern water column microbiota form genetic archives for paleoecological and paleoclimate reconstructions. The active microbiota will be determined based on their extremely labile messenger RNA (mRNA) and samples obtained during this study have to be kept frozen at temperatures below -80 ºC until further analysis to prevent degradation of RNA. Such delicate samples suitable for RNA work are not available elsewhere and funding is also requested to guarantee the appropriate sampling and transport conditions. The results to be obtained from these samples will be of great importance for microbiologists as well as the scientific “paleocommunity” and subsamples will also be available for other WHOI researchers who are interested in the Black Sea such as Dr. Katrina Edwards who is interested in magnetotactic bacteria from the redoxcline