Carbonate Chemistry Through a Transect of the North Pacific: Particle Fluxes and Dissolution Patterns

The North Pacific Ocean has been a sort of bellwether site for investigations of OA impact on ocean ecosystems. On a transect cruise from Oahu, Hawaii to Seward, Alaska in August, 2017, we conducted/deployed CTD/Niskin casts, floating traps, in situ carbonate dissolution incubators, in situ pumps, net tows and benthic sampling to examine carbonate chemistry and carbonate particle dynamics in this ocean section. We documented changes in water column carbonate chemistry as we traveled from the Subtropical gyre, through the transition zone (30-50° N) and into the Subpolar gyre. We present export PIC fluxes (0.2-0.7 mmol/m2d in the Subtropical to 1-2 mmol/m2d in the Subpolar) divided into fractions calcite and aragonite and have distributions of coccolithophores (cell numbers and species distribution) and foraminifera along this transect as well. Our measurement of in situ and laboratory CaCO3 dissolution rates cannot account for the loss of PIC that we see occurring in the upper 1000 m (as evidenced in flux attenuation and water column isotope budgets). However, the association of carbonic anhydrase (CA) activity with POC concentration has been documented and may, through the proven enzymatic enhancement of dissolution kinetics, be responsible for some portion of PIC dissolution in the upper ocean. This may occur on the sea floor as well as CA activity was also detected in the sediment column. We use a C isotope mass balance and mixing equation to define the contribution of carbonate dissolution and POC respiration to the DIC pool in N. Pacific ocean water masses.