Comparative behavior and distribution of biologically relevant trace metals - iron, manganese, and copper in four representative oxygen deficient regimes of the world's oceans

• Main Author: Vedamati, Jagruti
• Format: Dataset
• Language: English
• Published: University of Southern California Digital Library (USC.DL) 2015
• Subjects: Ocean Sciences; iron; copper; manganese; trace metals; oxygen minimum zones; denitrification; Arctic; Pacific
• Online Access: https://dx.doi.org/10.25549/usctheses-c3-305640; https://digitallibrary.usc.edu/asset-management/2A3BF163UXYA

This thesis explores the behavior and distribution of key redox sensitive elements - Fe and Mn under spatially varied suboxic conditions along eastern boundary upwelling regions as compared to that of the non-redox sensitive, bioactive trace metal - Cu. The response of these metals was then analyzed in a different non-oxygen minimum zone (OMZ) setting along Line P to compare and analyze the differences in distribution, if any caused by the suboxic conditions. Fe, Cu and Mn were investigated in the three major OMZs of the world’s oceans -- namely, the eastern tropical south Pacific off the coasts of Peru and Chile, the Arabian Sea and in the Costa Rica Upwelling Dome in eastern tropical north Pacific. For the non-OMZ sampling site, we sampled across a dynamic, high productivity region in the North East sub-arctic Pacific along Line P. ❧ Total dissolved Fe, Cu and Mn concentrations were determined using inductively coupled plasma mass spectrometry (ICP-MS). Fe (II) concentrations were determined using an automated flow injection analysis system. Results from the Peruvian OMZ indicate that Mn is largely decoupled from Fe. While Fe concentrations were very high on the shelf, it decreased drastically offshore and was coupled to redox conditions. In contrast, Mn concentrations were lower over the shelf and were often higher offshore, especially in surface waters. Results suggest that Mn is efficiently transported away from the highly reducing conditions of the shelf because of slow oxidation kinetics -- in contrast to Fe. In nearshore stations, off the broad continental shelf along the northern and central transects off Peru, exceedingly high Fe were measured with most of the dissolved Fe present as Fe(II) below the oxycline. Along the narrower southern Peruvian shelf, dissolved Fe concentrations were 10-fold lower. ❧ Cu distribution in the OMZs showed some interesting features observed for the first time. In transects through the Arabian Sea OMZ and off of Peru, a distinct draw down in Cu concentrations was observed at mid-depths coincident with the secondary nitrite maximum (SNM) while no such feature was present in stations outside the denitrification zone. Distributions along Line P suggest that one of the most striking differences in Fe & Mn distribution was the presence of high Mn: Fe ratios off the continental shelf along Line P as compared to those obtained in transects off the Peruvian coast. Complex redox cycling of Fe and Mn in the reducing sediments along the continental margin underlying the Peruvian OMZ results in the “Fe trapping” while Mn diffuses off shore into the water column, thereby resulting in lower DMn values along the Peruvian continental shelf. No distinct subsurface Fe plume was present throughout the transect along Line P. Cu depth profiles along Line P exhibit general features of a nutrient like element and agree with previous data from the central North Pacific. However, in the absence of a SNM along Line P, no draw down of Cu was observed at mid-depths similar to Cu distributions within the Arabian Sea OMZ. ❧ Overall, this thesis adds to our understanding of the effect of redox conditions within the suboxic zones on redox sensitive elements – Fe and Mn. It also furthers the knowledge of the behavior and distribution of important, biologically relevant trace metals -Fe, Mn and Cu in the world’s oceans.