Abstract
Marine oxygen minimum zones (OMZs) trap greenhouse gases, reduce livable habitats, a critical factor for these changes is the amount of dissolved oxygen (DO). The frequently used tool to reconstruct DO values, the Benthic Foraminifera Oxygen Index (BFOI), showed major shortcomings and lacks effectiveness. Therefore, we enhanced the BFOI and introduce enhanced BFOI (EBFOI) formulas by using all available data benthic foraminifers provide, calculating the whole livable habitat of benthic foraminifers, including bottom water oxygenation (BWO) and pore water oxygenation (PWO). Further, we introduce for the first time a transfer function to convert EBFOI vales directly into DO values, increasing efficiency by up to 38%. All formulas are calibrated on modern samples and applied to fossil datasets. Our new approach provides a major improvement in defining and reconstructing marine oxygen levels and eutrophication, by, providing a new toolset for understanding past changes and tracking actual and predicted future expanding OMZs.
Highlights
The ocean covers about 97% of the Earth’s physical habitat s pace[1]
In order to calculate (E)Benthic Foraminifers Oxygen Index (BFOI) values, benthic foraminifers are separated into three groups: "oxic" (O; > 1,5 ml/l), "suboxic" (S; 1.5–0.3 ml/l) and "dysoxic" (D; 0.3–0.1), based on extant literature data on oxygen requirements of foraminifers
A major offset towards overestimating oxic conditions, considerably increasing if high numbers of suboxic indicators are present within the samples, between qualitative data and calculated BFOI values was realized for the fossil datasets [e.g., the dataset of K ranner[71]; Fig. 2]
Summary
The ocean covers about 97% of the Earth’s physical habitat s pace[1]. changes in ocean chemistry and biodiversity and their faster response to physical and atmospheric changes affect the terrestrial realm and should be observed closely[2]. With expanding OMZs, methane accumulations move closer to zones of atmospheric exchange, drastically speeding up global warming by releasing this potent greenhouse g as[18,19,20,21,22,23] This process emphasizes the importance of dissolved oxygen as one of the most important environmental variables, and reconstructing changes of oxygen conditions for recent and geological times garnered much interest (Refs.[24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44]). Kaminski tested the BFOI for Mediterranean water masses using 30 samples from the Marmara S ea[33]
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