Year of Award

2017

Document Type

Thesis

Degree Type

Master of Interdisciplinary Studies (MIS)

Degree Name

Interdisciplinary Studies

Department or School/College

Interdisciplinary Studies Program

Committee Chair

Micheal D. DeGrandpre

Commitee Members

Michael D. DeGrandpre, J.B.A. Sandy Ross, Bradley E. Layton, James C. Beck

Keywords

ocean acidification, drifter, spectrophotometric, pH

Subject Categories

Chemical Engineering | Environmental Chemistry | Geochemistry | Mechanical Engineering

Abstract

Since the Industrial Revolution, the world's oceans have absorbed increasing amounts of CO2 and the resultant changes to the marine carbonate chemical system have reduced the pH by > 0.1 units (~ 30%) in surface waters. This acidification of the oceans has many far reaching impacts on marine life and there is great need of quality instrumentation to assess and follow the changing carbonate system. This MIS project aims to develop a low cost pH sensor with high precision and accuracy for open sea measurements with special emphasis on reduced size and cost. Design effort is based on the commercially available in situ ocean pH sensor, the SAMI-pH. Emphasis on small size and low cost will allow deployment of the sensors on a much wider variety of platforms than are currently viable thus greatly extending the spatial and temporal resolution of ocean acidification measurements. One such platform is NOAAs Global Drifter Program, a network of non-recovered drifting buoys that has potential for ocean carbon cycle research. A prototype instrument was designed, the inexpensive SAMI-pH or iSAMI-pH. This instrument was entered into the Wendy Schmidt Ocean Health (WSOH) XPRIZE. This was an incentivized global competition to spur innovation in pH sensor technology with both accuracy and affordability prize purses totaling $2 million dollars. The affordability purse consisted of three phases of testing that explored accuracy, precision and stability using a variety of tests that spanned 6 months. It progressed from bench testing in a temperature controlled chamber and a 60 day tank test at the Monterey Bay Aquarium Research Institute (MBARI), to a month long deployment in a specially designed tank at the Seattle Aquarium that used the highly variable waters of Puget Sound. In lab testing, the iSAMI showed ± 0.01 accuracy. In the MBARI test tank, the iSAMI showed precision of ± 0.004 pH units and stability of 0.008 pH units per month with validation uncertainty of ± 0.009 pH units. In the coastal trials, the iSAMI again showed a precision of ± 0.004 pH units and a stability of 0.011 pH units per month with a validation uncertainty of ± 0.012 pH units. Stability or drift was statistically indistinguishable from that of the validation measurements. The iSAMI was in excellent agreement with the commercially available SAMI-pH which won the accuracy prize purse of the WSOH XPRIZE. The iSAMI won the affordability prize purse exceeding the performance metrics by several fold.

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© Copyright 2017 Reuben C. Darlington