Manganese in the west Atlantic Ocean in the context of the first global ocean circulation model of manganese

Abstract

Dissolved manganese (Mn) is a biologically essential element. Moreover, its oxidised form is involved in removing itself and several other trace elements from ocean waters. Here we report the longest thus far 17 500 km length full-depth ocean section of dissolved Mn in the West Atlantic Ocean, comprising 1320 data values of high accuracy. This is the GA02 transect that is part of the GEOTRACES programme, which aims to understand trace element distributions. The goal of this study is to combine these new observations with a new, state-of-the-art, modelling to give a first assessment of the main sources and redistribution of Mn throughout the ocean. To this end, we simulate the distribution of dissolved Mn using a global-scale circulation model. This first model includes simple parameterisations to account for the sources, processes and sinks of Mn in the ocean. Oxidation and (photo)reduction, aggregation, settling, as well as biological uptake and remineralisation by plankton, are included in the model. Our model provides, together with the observations, the following insights: -The high surface concentrations of manganese are caused by the combination of photoreduction and sources to the upper ocean. The most important sources are sediments, dust, and, more locally, rivers. -Observations and model simulations suggest that surface Mn in the Atlantic Ocean moves downwards into the southward flowing North Atlantic Deep Water (NADW), but because of strong removal rates there is no elevated concentration of Mn visible any more in the NADW south of 40 • N.-The model predicts lower dissolved Mn in surface waters of the Pacific Ocean than the observed concentrations. The intense Oxygen Minimum Zone (OMZ) in subsurface waters is deemed to be a major source of dissolved Mn also mixing upwards into surface waters, but the OMZ is not well represented by the model. Improved high resolution simulation of the OMZ may solve this problem.-There is a mainly homogeneous background concentration of dissolved Mn of about 0.10 nM to 0.15 nM throughout most of the deep ocean. The model reproduces this by means of a threshold on particulate manganese oxides of 25 pM, suggesting that a minimal concentration of particulate Mn is needed before aggregation and removal become efficient.-The observed distinct hydrothermal signals are produced by assuming both a strong source and a strong removal of Mn near hydrothermal vents.

An investigation of basin-scale controls on upper ocean export and remineralization

“…This study of the southeastern tropical Pacific has illustrated the benefit of cosampling for particulate trace metals and 234 Th and produced some of the first large-scale 234 Thderived flux and surface residence time estimates for trace metals in the global ocean. These flux and residence time estimates will help to close trace metal budgets for the Pacific Ocean and we anticipate that these data will aid in the improvement of current GBMs used to model dissolve and particulate trace metal distributions, especially in the Pacific OMZ, where GBMs struggle to reproduce in-situ distributions (van Hulten et al, 2017). The 234 Th-method for determining the residence time of trace metals in the surface ocean provides a useful alternative to dust-based estimates, where observation-based fluxes have been shown to disagree by two orders of magnitude in some cases (Anderson et al, 2016).…”

“…Because trace metals are necessary for many cellular functions and their abundance or scarcity can influence the BCP, it is important to quantify the surface export of these elements and understand the drivers of trace metal cycling in the upper ocean. Efforts to include metals in global biogeochemical models have illustrated our lack of understanding of the controls on trace metal distributions in the global ocean (Tagliabue et al, 2016;van Hulten et al, 2017) and the surface export estimates contained within Chapter 3 are a first step to improving these models.…”

“…However, a recent comparison of thirteen Fe-incorporating GBMs found that 'all models struggle to reproduce many aspects of the observed spatial patterns' (Tagliabue et al, 2016). For other metals, such as Mn and Al, good agreement between observed and modeled values have been achieved in select parts of the global ocean (van Hulten et al, 2017(van Hulten et al, , 2014(van Hulten et al, , 2013. However, each GBM still struggles to replicate certain processes (e.g.…”

The Relationships Between Dissolved Zinc and Major Nutrients Phosphate and Silicate Along the GEOTRACES GA02 Transect in the West Atlantic Ocean

“…This notion led us to design the 17,500-km-long GEOTRACES GA02 section of the Netherlands. For such interpretations along this West Atlantic section, both Ocean Biogeochemical Cycling Modelling (Middag, Séférian, et al, 2015;van Hulten et al, 2013van Hulten et al, , 2014van Hulten et al, , 2017 and extended optimal multiple parameter (eOMP) analysis have been applied. This offers the opportunity to assess the distribution of Zn and nutrients along the conduit of the southward traveling deep North Atlantic Deep Water (NADW) and the northward traveling waters of Antarctic origin.…”

A global scavenging and circulation ocean model of thorium-230 and protactinium-231 with realistic particle dynamics (NEMO–ProThorP 0.1)

“…This model has been employed for many other studies concerning trace metals, as well as large-scale ocean biogeochemistry (e.g. Gehlen et al, 2007;Arsouze et al, 2009;Dutay et al, 2009;Tagliabue et al, 2010;Van Hulten et al, 2013, 2017b. We force PISCES by a climatological year of circulation fields (including turbulent diffusion) that was obtained from the dynamical component of the Nucleus for…”