The PI request funding to undertake design improvements and complete the evaluation of an autonomous sensor for measurement of seawater total alkalinity (SAMI-alk). Total alkalinity (AT) is one of the four measureable dissolved inorganic carbon parameters and is therefore of paramount importance in the study of carbon cycling in the oceans. AT is commonly measured as part of shipboard hydrographic surveys and ocean time-series and has more recently become a critical parameter for ocean acidification studies. An autonomous AT sensor can be used in combination with other CO2 parameter sensors that are commercially available, i.e. pH and pCO2, to remotely quantify the inorganic carbon system. For example, if pH and AT are accurately measured, total dissolved inorganic carbon (DIC), carbonate, and CaCO3 saturation state can be calculated. Long-term mooring based quantification of these parameters is not yet possible. Through a previous NSF grant, we demonstrated that a novel titration methodology named Tracer Monitored Titration (TMT) could simplify AT analysis by eliminating the need for volumetric or gravimetric measurements required for conventional AT titrations. The SAMI-alk was tested both in the lab and during a cruise. The performance on the cruise was not as good as the laboratory tests. This proposal requests funds to complete the SAMI-alk development and evaluation.
Broader Impacts:
The ability to measure alkalinity is a key need for acidification research. If successful, the instrumentation development proposed here will provide an important tool for understanding the vulnerability and response of marine ecosystems to acidification. The PI has actively pursued commercialization of the autonomous instruments that he has developed in the past. Commercialization of the proposed alkalinity sensor through will greatly broaden the impacts of the technology, making it broadly available to the ocean sciences community. The project includes funding for on undergraduate student.
The objective of this NSF grant was to complete development of an autonomous alkalinity sensor for ocean applications named SAMI-alk. This development project was previously funded by NSF but had not yet succeeded in deploying the sensor. Alkalinity is the acid neutralizing capacity of water and is an important parameter for understanding the acid/base chemistry of seawater. Alkalinity measurements are widely used for quantifying the uptake of anthropogenic CO2 by the oceans and for determining the calcification rates (which changes alkalinity) of coral reefs and other organisms. An autonomous alkalinity sensor offers great potential for more effectively studying these processes because current technology is limited to ship or land-based laboratories. With this new technology scientists and other stakeholders will be able to continuously monitor these processes. The first two years of the grant were focused on improving the precision and accuracy of the instrument. We found that the solubility of the indicator we were using was causing some of the performance problems. A more solubile indicator (bromocresol purple) improved the performance. We also found that the instrument is sensitive to bubble formation at higher temperatures (due to degassing of CO2 from the sample as it is titrated). The bubbles are not a problem under hydrostatic pressure. The laboratory testing and improvements led to the successfull deployment (in 2013) of the SAMI-alk in a test tank in Oregon and on a buoy in Kaneohe Bay, Hawaii (see Figure below). These tests show that the instrument can perform well in harsh in situ conditions. The Hawaii buoy alkalinity time-series is the longest continue alkalinity data set ever collected and provides important insights into what conditions control coral reef productivity. This work has led to two scientific manuscripts, one focused on the technology (recently submitted to Environmental Science and Technology) and one focused on coral reef biogeochemistry (in preparation).
