Abstract

Abstract. Assessing changes in the marine carbon cycle arising from anthropogenic CO2 emissions requires a detailed understanding of the carbonate system's natural variability. Coastal ecosystems vary over short spatial and temporal scales, so their dynamics are not well described by long-term and broad regional averages. A year-long time series of pCO2, temperature, salinity, and currents is used to quantify the high-frequency variability of the carbonate system at the mouth of the Bay of Fundy, Nova Scotia. The seasonal cycle of pCO2 is modulated by a diel cycle that is larger in summer than in winter and a tidal contribution that is primarily M2, with amplitude roughly half that of the diel cycle throughout the year. The interaction between tidal currents and carbonate system variables leads to lateral transport by tidal pumping, which moves alkalinity and dissolved inorganic carbon (DIC) out of the bay, opposite to the mean flow in the region, and constitutes a new feature of how this strongly tidal region connects to the larger Gulf of Maine and northwest Atlantic carbon system. These results suggest that tidal pumping could substantially modulate the coastal ocean's response to global ocean acidification in any region with large tides and spatial variation in biological activity, requiring that high-frequency variability be accounted for in assessments of carbon budgets of coastal regions.

Highlights

  • Oceanic uptake of anthropogenic carbon dioxide (CO2) moderates the rise of atmospheric CO2 concentrations and leads to changes in the ocean carbon cycle

  • A year-long record of high-frequency measurements of pCO2 (Fig. 2a), temperature (Fig. 2b), and pressure, 4 months of salinity (Fig. 2c), and 1 month of velocity data were collected via a cabled-to-shore observatory on a bottom frame that was deployed in approximately 10.5 m mean water depth

  • Mary’s Bay and the Bay of Fundy, and because the water properties in these embayments can differ, the strong semi-diurnal (M2) tide causes tidal period variability in the carbonate system. pCO2 varies on annual, daily, and tidal timescales, and the magnitude of the daily and tidal signals changes with the season

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Summary

Introduction

Oceanic uptake of anthropogenic carbon dioxide (CO2) moderates the rise of atmospheric CO2 concentrations and leads to changes in the ocean carbon cycle. To the best of our knowledge, the tidal transport of carbon in this macrotidal system, or far from large freshwater or nutrient sources, has never been addressed To investigate this issue, a year-long, high-frequency time series of pCO2, temperature, salinity, and currents was measured via a cabled-to-shore platform in Grand Passage, a tidal channel at the mouth of the Bay of Fundy, Nova Scotia (Fig. 1). A year-long, high-frequency time series of pCO2, temperature, salinity, and currents was measured via a cabled-to-shore platform in Grand Passage, a tidal channel at the mouth of the Bay of Fundy, Nova Scotia (Fig. 1) This location is ideal for tracing the main input of water into the Bay from the Scotian Shelf. Tidal budgets have been estimated for oxygen from dissolved oxygen measurements

Measurements and data processing
Time series measurements
Bottle samples
Other data sources
Estimating alkalinity from salinity
Calculating DIC
Seasonal evolution of carbonate system variables
Unraveling daily and tidal cycles of biogeochemically driven changes in DIC
Tidal phasing
Lateral transport by tidal pumping
Air–sea CO2 flux
Consideration of the local DIC budget
Conclusions
Vertical mixing
Mean volume transport
Budget for biological DIC production
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