Comparison of in situ Particulate Organic Carbon Concentrations with Optical Properties in the Mesopelagic Regions of the Atlantic Ocean

The Ocean Biological Carbon Pump (OBCP) is a significant component of the global carbon cycle that contributes to the uptake of atmospheric carbon and is principally mediated by organic particles sinking from the euphotic zone to the deep ocean. This mechanism is capable of sequestering carbon on a quasi-permanent timescale and thus it impacts on the Earth’s climate. The OBCP could be transferring between 4 and 11 Gt C yr-1 into the ocean’s interior, and these large uncertainties arise largely from lack of observations.

Optical measurements from satellites and in situ autonomous platforms have the potential to improve our understanding of the magnitude and efficiency of the OBCP. The overall objective of our study is to compare simultaneous in situ measurements of optical properties and particulate organic carbon (POC) in the mesopelagic region of the Atlantic Ocean. Water samples for the study were collected during the research cruise “The Atlantic Meridional Transect 24” from the rosette at 6 depths for 67 stations, filtered through pre-combusted Whatman GF/F filters, flash frozen in liquid nitrogen and stored at -80 degrees C. POC was then determined in the laboratory using a CHN analyzer. We will present the resulting POC values and describe their relationships with in situ optical measurements focusing on the relatively unexplored mesopelagic region. We will also present a detailed analysis of the measurement uncertainties based on the blanks and replicates collected during the cruise.