The study of dynamic biogeochemical processes in the ocean, especially in the deep ocean or near hydrothermal vents, is a daunting challenge and requires the ability to monitor a variety of chemical species in-situ in real time under extreme conditions. Understanding these dynamic processes is critical for our ability to predict and/or mitigate the long term effects of natural and human impacts on the oceans. The propose to develop and demonstrate a prototype ion selective electrode (ISE) sensor array capable of providing simultaneous in-situ real-time measurements of a variety of ionic chemical species at extreme depths and near vent temperatures in the ocean. The proposed sensor array will be based on the ISE sensor array that was designed, built, tested, and successfully used on the surface of Mars as part of the 2007 Phoenix Mars Mission, to analyze for ionic species in an aqueous solution containing a soil sample
The longer term objective of this initial effort is to enable follow-on research that, with improved detection limits and selectivity, will provide the ocean sciences community with a new tool for in-situ real-time mapping of a broad range of chemical species in seawater. The resulting sensor array device will also be of use to researchers in a variety of related disciplines for studies or monitoring of other bodies of water such as lakes, estuaries, ground water, drinking water, and rivers.
Broader Impacts:
The development of an innovative research tool to enable in-situ temporal and spatial monitoring of the chemical properties of oceanic waters represents an enormous contribution to the fields of environmental and analytical chemistry. Clearly, this project if successful will enable a charting of ocean circulation, measurements of carbon dioxide levels in the ocean, and studies of the impacts of these on climate change research. The outreach program will engage teachers and students in summer field studies to monitor waters at the mouth of the Charles River in Boston Bay and/or the Delaware Estuary, and the anoxic Delaware Inland Bays. These will provide enormous intangible, yet demonstrable outcomes and impacts of the research. Three graduate students are involved in this project. In addition, the project will provide opportunities for undergraduate student from a broad range of disciplines to participate in the design and development of in situ instrumentation. High-school students will also be involved, through the participation of classrooms to field tests and to a summer field trip, involving the graduate students supported by the project. Public outreach is also mentioned, through the realization of videos by classrooms.
In this project, we demonstrated that the best way to test the viability of an instrument for ocean and estuarine research over a wide range of concentrations is to do perform the tests in real time or aboard ship as quickly as possible. For this project, we tested the ISE package from Tufts University and other sensors from the University of Delaware for intercomparison in estuarine (Delaware and Chesapeake Bays), coastal and deep ocean waters (3000m) off the continental shelf of Delaware. The Delaware Bay estuary from Philadelphia to the mouth of the Bay showed a salinity range from freshwater to 32 salinity units (90 % of open ocean salinity). The Chesapeake Bay has seasonal summer low oxygen conditions (anoxia) ranging from not detectable in the bottom waters to 100 % oxygen saturation in surface waters as well as hydrogen sulfide in the bottom waters. This oxygen condition is stabilized by an increase in salinity from surface to bottom and a decrease in temperature from surface to bottom. The Atlantic Ocean waters off the continental shelf show less change in salinity and oxygen but show an increase in nitrate and other nutrients from surface to bottom waters and permit testing of real time equipment under significant pressures at ocean depth. These three marine systems were shown to be ideal for testing of analytical methods and equipment. In this study, our group collected in situ or real time data with our in situ electrochemical analyzer for intercomparison purposes. In addition, a biological sensor called the Fluorescence Induction and Relaxation System (FIRe) was mated with our analyzer, a conductivity-temperature-depth (CTD) sensor and a pump to send water to the ship for further analytical measurements (photo in Figure 1). The FIRe measures the health of phytoplankton or algae at photosystem center II where plants produce oxygen by performing fluorescence measurements over short time periods (microseconds or less). When the algae are stressed, these measurements show a dramatic decrease as shown in the plot on the right in Figure 1. During 2011 in the Chesapeake Bay, algae were stressed when they were in contact with waters containing hydrogen sulfide. However, in 2012, algae were not stressed as hydrogen sulfide was not detectable. Laboratory experiments with pure cultures verified these real time data and showed that the longer the time that algae remained in contact with hydrogen sulfide, the more stressed they became. The coupling of biological, chemical and physical sensors is an excellent way to study ecosystem health at the planktonic level.
