Abstract
The Bermuda Testbed Mooring (BTM) and Bay of Bengal Ocean Acidification (BOBOA) mooring measurements were used to identify changes in the partial pressure of CO2 at the sea surface (pCO2sea) and air-sea CO2 fluxes (FCO2) associated with passage of two tropical cyclones (TCs), Florence and Hudhud. TC Florence passed about 165 km off the BTM mooring site with strong wind speeds of 24.8 m s–1 and translation speed of 7.23 m s–1. TC Hudhud passed about 178 km off the BOBOA mooring site with wind speeds of 14.0 m s–1 and translation speed of 2.58 m s–1. The present study examined the effect of temperature, salinity, dissolved inorganic carbon (DIC), total alkalinity (TA), air-sea CO2 flux, and phytoplankton chlorophyll a change on pCO2sea as a response to TCs. Enhanced mixed layer depths were observed due to TCs-induced vertical mixing at both mooring sites. Decreased pCO2sea (–15.16±5.60 μatm) at the BTM mooring site and enhanced pCO2sea (14.81±7.03 μatm) at the BOBOA mooring site were observed after the passage of Florence and Hudhud, respectively. Both DIC and TA are strongly correlated with salinity in the upper layer of the isothermal layer depth (ILD). Strong (weak) vertical gradient in salinity is accompanied by strong (weak) vertical gradients in DIC and TA. Strong vertical salinity gradient in the upper layer of the ILD (0.031 psu m–1), that supply much salinity, dissolved inorganic carbon and total alkalinity from the thermocline was the cause of the increased pCO2sea in the BOBOA mooring water. Weak vertical salinity gradient in the upper layer of the ILD (0.003 psu m–1) was responsible for decreasing pCO2sea in the BTM mooring water. The results of this study showed that the vertical salinity gradient in the upper layer of the ILD is a good indicator of the pCO2sea variation after the passages of TCs.
Highlights
Anthropogenic CO2 emissions play an important role in global climate change
At the Bay of Bengal Ocean Acidification (BOBOA) mooring site, the increased pressure of CO2 at the sea surface (pCO2sea) after tropical cyclones (TCs) Hudhud was mainly due to the strong vertical salinity gradient in the upper layer of the isothermal layer depth (ILD) (0.031 psu m–1) that determined the supply of much salinity, dissolved inorganic carbon (DIC) and total alkalinity (TA) from the thermocline. This salinity related increase in pCO2sea basically compensated for the contribution of sea surface temperature (SST) decrease. As both DIC and TA are strongly correlated with salinity, and the strong vertical gradient in salinity is accompanied by the strong vertical gradients in DIC and TA, we propose that the magnitude of the vertical salinity gradient in the upper layer is a good indicator of the pCO2sea variation after the passage of TC
The present study examined various contributing factors that induced the change of pCO2sea following TCs “wind-pump” over the North Atlantic Ocean (Florence, 3–12 September 2006) and Bay of Bengal (BoB) (Hudhud, 8–11 October 2014) using mooring buoy measurements
Summary
Anthropogenic CO2 emissions play an important role in global climate change. About 30% of the anthropogenic CO2 has been stored in the ocean [1]. Variation of pCO2 concentrations induced by tropical cyclones in the oceans.
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