“Sources and Distribution of Suspended Particulate Matter (SPM) Using Stable Isotopes In The Central Arabian Gulf”

Abstract

Suspended Particulate matter (SPM) (>0.45µm) plays a significant role in the global carbon cycle. Hence, we measured changes in concentrations of SPM with depth and at distances from shore in the exclusive economic zone of Qatar (EEZ). Signatures of stable isotopic analysis and elemental composition of organic carbon and nitrogen were used to assess sources of SPM during summer of 2019. Samples of SPM were collected from three transects crossing the EEZ representing different depths. Hydrodynamic parameters including salinity, density, water temperature, and DO were measured to assess effects of different water masses on the distribution of the SPM. The study investigated the relation between Chl-a concentration and SPM in order to identify the non-algal SPM sources. The isotopic composition of SPM showed a distinct carbon isotope depletion and a relative nitrogen enrichment, except for a few locations were nitrogen was depleted (δ15N ~ 0). The dissolved nutrients and chlorophyll-a showed distinct trends with depth and with distance from shoreline. Trends of Chl-a indicated that the shallow central Arabian Gulf is relatively productive with high chlorophyll-a and nutrients at the shallower sites within 40 km from the coastline. The SPM’s stable isotope composition confirmed that phytoplankton is a prominent source for SPM in the Gulf with an average δ13C of about 18.56 ‰. On the other hand, δ15N signatures in SPM showed that nitrogen from nitrogen-fixation play a significant role in supporting new nitrogen sources and primary productivity in the central Arabian Gulf at the north eastern region of the EEZ of Qatar.