Award: OCE-1259055

The ocean plays an important role in moderating current and future changes to the earthÆs climate by adsorbing or taking up carbon dioxide (CO2) out of the atmosphere. The result of which reduces the rate at which CO2 accumulates in the atmosphere and the consequential warming of our planet. There are regions in the western portion of North Pacific Ocean where the ocean uptake of CO2 is particularly pronounced. A primary goal of our research was to find out what processes caused this enhanced rate of CO2 uptake. There are two likely processes, photosynthesis by plankton and ocean circulation, which result in ocean uptake of CO2. We used measurements of certain chemicals in seawater that can identify or fingerprint photosynthesis and be used to determine the rate at which it is occurring in the ocean. These chemical species included dissolve gases like CO2, oxygen (O2) and the rarer isotopic component of these gases (13CO2 and 18O2, 17O2). We obtained seawater samples on which to measure these chemicals through a collaboration with a container ship company (Orient Overseas Container Line) who allowed us to collect surface seawater samples on their ships as they transited between Hong Kong and Long Beach, CA. The results of our measurements indicated that the photosynthesis rate increased westward across the North Pacific by almost two-fold. However, a surprising result was that this increased photosynthesis rate did not result in an increased rate of CO2 uptake. The reason was that the depth of the surface mixed layer also increased westward by an even greater factor of three-fold which enhanced the bacterial respiration rate more than the photosynthesis rate. We found that the reason for the enhanced CO2 uptake rate in the western North Pacific was a result mainly of circulation. The most plausible scenario is that the Kuroshio Current, a strong Gulf Stream like current in the North Pacific Ocean, carries warm CO2 depleted surface water northward and then cools and carries high CO2 water eastward which causes a net removal of CO2 from the surface layer of the western North Pacific Ocean. This removal of CO2 from the surface ocean enhances the uptake of CO2 from the atmosphere in this region. The importance of this research is that both marine photosynthesis and ocean circulation will likely change in the future as the earth and ocean warm. Thus global warming will likely impact the rate at which the ocean removes CO2 from the atmosphere. What we donÆt yet know is whether this æfeedbackÆ will increase or decrease the rate of ocean uptake of atmospheric CO2 and thus accelerate or slow the rate of global warming. Last Modified: 07/01/2016 Submitted by: Paul D Quay