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Takeshita, Y, Cyronak T, Martz TR, Kindeberg T, Andersson AJ.  2018.  Coral reef carbonate chemistry variability at different functional scales. Frontiers in Marine Science. 5   10.3389/fmars.2018.00175   AbstractWebsite

There is a growing recognition for the need to understand how seawater carbonate chemistry over coral reef environments will change in a high-CO2 world to better assess the impacts of ocean acidification on these valuable ecosystems. Coral reefs modify overlying water column chemistry through biogeochemical processes such as net community organic carbon production (NCR) and calcification (NCC). However, the relative importance and influence of these processes on seawater carbonate chemistry vary across multiple functional scales (defined here as space, time, and benthic community composition), and have not been fully constrained. Here, we use Bermuda as a case study to assess (1) spatiotemporal variability in physical and chemical parameters along a depth gradient at a rim reef location, (2) the spatial variability of total alkalinity (TA) and dissolved inorganic carbon (DIC) over distinct benthic habitats to infer NCC:NCP ratios [< several km(2); rim reef vs. seagrass and calcium carbonate (CaCO3) sediments] on diel timescales, and (3) compare how TA-DIC relationships and NCC:NCP vary as we expand functional scales from local habitats to the entire reef platform (10's of km(2)) on seasonal to interannual timescales. Our results demonstrate that TA-DIC relationships were strongly driven by local benthic metabolism and community composition over diel cycles. However, as the spatial scale expanded to the reef platform, the TA-DIC relationship reflected processes that were integrated over larger spatiotemporal scales, with effects of NCC becoming increasingly more important over NCR. This study demonstrates the importance of considering drivers across multiple functional scales to constrain carbonate chemistry variability over coral reefs.

Gonski, SF, Cai WJ, Ullman WJ, Joesoef A, Main CR, Pettay DT, Martz TR.  2018.  Assessment of the suitability of Durafet-based sensors for pH measurement in dynamic estuarine environments. Estuarine Coastal and Shelf Science. 200:152-168.   10.1016/j.ecss.2017.10.020   AbstractWebsite

The suitability of the Honeywell Durafet to the measurement of pH in productive, high-fouling, and highly-turbid estuarine environments was investigated at the confluence of the Murderkill Estuary and Delaware Bay (Delaware, USA). Three different flow configurations of the SeapHOx sensor equipped with a Honeywell Durafet and its integrated internal (Ag/AgCl reference electrode containing a 4.5 M KCl gel liquid junction) and external (solid-state chloride ion selective electrode, CI-ISE) reference electrodes were deployed for four periods between April 2015 and September 2016. In this environment, the Honeywell Durafet proved capable of making high-resolution and high-frequency pH measurements on the total scale between pH 6.8 and 8.4. Natural pH fluctuations of >1 pH unit were routinely captured over a range of timescales. The sensor pH collected between May and August 2016 using the most refined SeapHOx configuration exhibited good agreement with multiple sets of independently measured reference pH values. When deployed in conjunction with rigorous discrete sampling and calibration schemes, the sensor pH had a root-mean squared error ranging between 0.011 and 0.036 pH units across a wide range of salinity relative to both pH(T) calculated from measured dissolved inorganic carbon and total alkalinity and pH(NBs) measured with a glass electrode corrected to pH(T) at in situ conditions. The present work demonstrates the viability of the Honeywell Durafet to the measurement of pH to within the weather-level precision defined by the Global Ocean Acidification Observing Network (GOA-ON, <= 0.02 pH units) as a part of future estuarine CO2 chemistry studies undertaken in dynamic environments. (C) 2017 Elsevier Ltd. All rights reserved.