Nicolaas Glock

The response of benthic Foraminifera to low-oxygen conditions of the Peruvian oxygen minimum zone

Recent benthic foraminifera and their distribution in surface sediments were studied on a transect through the Peruvian oxygen minimum zone (OMZ) between 10 and 12°S. The OMZ with its steep gradients of oxygen concentrations allows determinations of the oxygen-dependent changes of species compositions in a relatively small area. Our results from sediments of 13 multicorer stations from 79 to 823 m water depth demonstrate that calcareous species, especially bolivinids, dominate the assemblages throughout the OMZ. The depth distribution of several species matches distinct ranges of bottom water oxygen levels. The distribution pattern inferred a proxy which allows estimating dissolved oxygen concentrations for reconstructing oxygen levels in the geological past.

The functionality of pores in benthic Foraminifera and bottom water oxygenation: a review

This chapter will give a brief review about the present understanding of pores in tests of benthic foraminifera. The interpretation of the pore function changed through time, and a couple of theories were proposed. The research about the functionality of pores recently became of new interest because it seems likely that they are involved in the respiration pathways of some benthic foraminifera. The fact that several benthic species are able to survive anoxia points out the importance for a better understanding of these respiration pathways and which adaptions differentiate these species from species which cannot survive in oxygen-depleted habitats. Nitrate respiration seems to be widespread among foraminifera from oxygen-depleted habitats, and thus knowledge if and in how far the pores are involved in the process of denitrification would help to understand the process of denitrification in eukaryotic foraminiferal cells.

A Novel Eukaryotic Denitrification Pathway in Foraminifera

Summary Benthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. Large-scale genome and transcriptomes analyses reveal the presence of a denitrification pathway in foraminifera species of the genus Globobulimina. This includes the enzymes nitrite reductase (NirK) and nitric oxide reductase (Nor) as well as a wide range of nitrite/nitrate transporters (Nrt). A phylogenetic reconstruction of the enzymes’ evolutionary history uncovers evidence for an ancient acquisition of the foraminiferal denitrification pathway from prokaryotes. We propose a model for denitrification in foraminifera where a common electron transport chain is used for anaerobic and aerobic respiration. The evolution of hybrid respiration in foraminifera likely contributed to their ecological success, which is well documented in palaeontological records since the Cambrian period.

Coupling of oceanic carbon and nitrogen facilitates spatially resolved quantitative reconstruction of nitrate inventories

Anthropogenic impacts are perturbing the global nitrogen cycle via warming effects and pollutant sources such as chemical fertilizers and burning of fossil fuels. Understanding controls on past nitrogen inventories might improve predictions for future global biogeochemical cycling. Here we show the quantitative reconstruction of deglacial bottom water nitrate concentrations from intermediate depths of the Peruvian upwelling region, using foraminiferal pore density. Deglacial nitrate concentrations correlate strongly with downcore δ13C, consistent with modern water column observations in the intermediate Pacific, facilitating the use of δ13C records as a paleo-nitrate-proxy at intermediate depths and suggesting that the carbon and nitrogen cycles were closely coupled throughout the last deglaciation in the Peruvian upwelling region. Combining the pore density and intermediate Pacific δ13C records shows an elevated nitrate inventory of >10% during the Last Glacial Maximum relative to the Holocene, consistent with a δ13C-based and δ15N-based 3D ocean biogeochemical model and previous box modeling studies.Understanding controls on past nitrogen budgets can improve predictions for future global biogeochemical cycling. Here, using foraminiferal pore density and δ13C, the authors present a quantitative record of deglacial nitrate from the intermediate Pacific and infer close coupling between carbon and nitrogen cycles.

A 22 kyr record of an evolving mid-depth hiatus in sediments at the Peruvian margin

The Peruvian coastal region has long been in the focus of marine geological investigations because of its importance to understand high productivity areas and the oxygen minimum zones (OMZs) in today’s and past oceans. The reconstruction of paleoenvironmental conditions for periods since the Last Glacial Maximum was hampered by a ubiquitous hiatus in sediment core records. We combined the stratigraphical information of 22 sediment cores from the literature and own results from 9 cores collected during R/V Meteor cruises M77/1 and M77/2 as a part of Sonderforschungsbereich 754. The cores were located between 3° and 18S and water depths of 90 to 1300 m within and below the Peruvian OMZ. In general, Peruvian Margin sediments consisted of olive green to greyish green silty clays predominantly showing laminations within the OMZ. Diatomaceous oozes were occasionally found underneath the main upwelling areas. Homogenously bioturbated silty clays with planktonic foraminifera were found around the OMZ in particular in the northern part of the region. Cores obtained from south of 7S showed slumping, erosional surfaces, phosphorite sands and unconformities. In order to investigate the distribution of the hiatus in space and time, we compared the lithologies of the cores of the corresponding time intervals; Late Holocene, Early Holocene, Bølling/Allerød, HeinrichStadial 1 and Last Glacial Maximum with the Recent conditions. Each time interval showed abundant unconformities successively progressing along the continental slope from south to north during the deglaciation. It has been suggested that the erosion and concomitant non-deposition was caused by the poleward undercurrent (PCUC: Peru Chile Undercurrent) (Reimers and Suess, 1983; Reinhardt et al., 2002 and the references therein) which today feeds the upwelling in the region. The PCUC originates around 5-7°S and is centred between 50 and 400 m water depth, with a well-defined core around 100 to 300 m. The undercurrent reaches its highest velocities around 10°S and leads to partial erosion along the shelf. In addition to the PCUC, breaking internal waves affect sedimentation and shape the slope at greater depths between 500 and 700 m around 11S (Mosch et al., 2012). Both, undercurrent and internal waves created erosional surfaces, non-deposition and slumps, evolving and affecting a wider area with the onset of Termination I.