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Coastal signals of environmental changes: foraminifera as benthic monitors

Brinkmann, Inda LU orcid (2022) In LUNDQUA
Abstract
Climate changes, tightly linked to anthropogenic activities, are significantly altering environments and ecosystems globally, such as by increasing marine and coastal deoxygenation or occurrences of extreme weather events. The significance of paleoenvironmental and -climate reconstructions, as well as monitoring of current conditions, for unravelling baseline natural variation, today’s changes and potential future impacts, has been recognised by the Intergovernmental Panel on Climate Change (IPCC) reports. However, to access past records of physical and chemical environmental variables, and comprehensively assess ecosystem reactions, reliable and sensitive proxies are critical.

This thesis’ focus lies on benthic... (More)
Climate changes, tightly linked to anthropogenic activities, are significantly altering environments and ecosystems globally, such as by increasing marine and coastal deoxygenation or occurrences of extreme weather events. The significance of paleoenvironmental and -climate reconstructions, as well as monitoring of current conditions, for unravelling baseline natural variation, today’s changes and potential future impacts, has been recognised by the Intergovernmental Panel on Climate Change (IPCC) reports. However, to access past records of physical and chemical environmental variables, and comprehensively assess ecosystem reactions, reliable and sensitive proxies are critical.

This thesis’ focus lies on benthic foraminifera—unicellular protists with mineralised or organic test, abundantly inhabiting ocean and coastal sediments—and their calibration as indicator for a variety of environmental conditions in field-sampling approaches. The research projects follow two general strategic tracks: (I) a biogeochemical assessment of trace-elemental ratios in foraminiferal calcium-carbonate tests using high-resolution, micro-analytical techniques; (II) a molecular approach investigating foraminiferal environmental DNA derived from coastal sediments.

Papers I and II concern the calibration of the benthic foraminiferal Mn/Ca proxy for marine oxygenation conditions in modern field studies. Trace-element concentrations and distributions were measured by plasma-, laser- and synchrotron-based analyses in a high-resolution, individual-foraminifera approach, and interpreted in the context of ambient physical and chemical conditions of the water column, pore-waters and sediments (including oxygen and manganese concentrations). Investigating two coastal systems with almost permanently severely oxygen-deficient bottom-waters (Santa Barbara Basin, Paper I), and undergoing a seasonal oxygenation cycle across the low- to well-oxygenated range (Gullmar Fjord, Paper II), respectively, demonstrated the utility of the Mn/Ca proxy for indicating low-oxygen conditions specifically. Continued calibration efforts under consideration of ambient oxygenation and redox regimes may open further possibilities of quantitative oxygen reconstructions. Paper III explores the use of coastal, benthic Ba/Ca records as indicator of riverine runoff and drought on land across the years 2018 and 2019, characterised by severe heat and drought, and warm and wet conditions, respectively. Benthic Ba/Ca correlated significantly with the hydroclimate conditions, as inferred from extensive meteorological and hydrological data sets of the region, highlighting qualitative proxy potential for paleo-drought reconstructions. Based on ambient sediment and pore-water geochemistry, we discuss mediation of water-column transport and pore-water Ba cycling by Fe and Mn oxides. All three investigations of these geochemical proxies (Paper I–III) highlighted the significance of biological controls on foraminiferal TE/Ca, which are species-specific and, thus, should be a deciding factor in choosing proxy candidate species. In particular the influences of micro-habitat distribution and utilised metabolic pathways by foraminifera are discussed in detail.

In Paper IV foraminiferal biodiversity and assemblage responses to natural and anthropogenic environmental trends in a fjord system (Swedish west coast) are documented in a metabarcoding approach. Environmental DNA successfully tracked biodiversity and community composition changes associated with contrasting ecosystems but showed damped sensitivity to environmental variability on sub-annual time-scales. Overlaps and discrepancies between molecular and traditional, observation-based assessment techniques, as well as future trajectories to resolve uncertainties are discussed.

Overall, this thesis solidifies and expands the currently available proxy toolbox for reconstructions of both coastal low-oxygen, as well as terrestrial hydroclimate conditions. The findings contribute towards filling current knowledge gaps pertaining to biotic impacts on foraminifera-derived biogeochemical signals and methodological uncertainties in metabarcoding approaches and highlight the significance of implementing molecular techniques in conventional foraminiferal assemblage studies. (Less)
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author
supervisor
opponent
  • Professor Kucera, Michal, MARUM, University of Bremen, Germany
organization
publishing date
type
Thesis
publication status
published
subject
keywords
benthic foraminifera, proxy calibration, trace element geochemistry, environmental DNA, deoxygenation, drought, coastal environments
in
LUNDQUA
issue
93
pages
184 pages
publisher
Lund University
defense location
Pangea, Department of Geology, Sölvegatan 12, Lund. Join via Zoom: https://lu-se.zoom.us/j/63307114489?pwd=OGpQcElDL0toT1I5M2h1RFFKTmNrdz09 password: 365795
defense date
2022-10-21 09:15:00
ISBN
978-91-87847-66-0
978-91-87847-67-7
project
Tracing past bottom water oxygenation in the sea: a microanalytical approach to improve calcium carbonate based proxies (TOPICaL)
Tracing coastal bottom-water oxygenation: a microanalytical approach to improve calcium carbonate based proxies
Tracing past bottom-water oxygenation in the sea: a microanalytical approach to improve calcium carbonate-based proxies
language
English
LU publication?
yes
id
fe1425d7-7f50-40d1-a28f-0ecf5d177bc0
date added to LUP
2022-09-10 12:29:34
date last changed
2023-02-23 15:10:39
@phdthesis{fe1425d7-7f50-40d1-a28f-0ecf5d177bc0,
  abstract     = {{Climate changes, tightly linked to anthropogenic activities, are significantly altering environments and ecosystems globally, such as by increasing marine and coastal deoxygenation or occurrences of extreme weather events. The significance of paleoenvironmental and -climate reconstructions, as well as monitoring of current conditions, for unravelling baseline natural variation, today’s changes and potential future impacts, has been recognised by the Intergovernmental Panel on Climate Change (IPCC) reports. However, to access past records of physical and chemical environmental variables, and comprehensively assess ecosystem reactions, reliable and sensitive proxies are critical. <br/><br/>This thesis’ focus lies on benthic foraminifera—unicellular protists with mineralised or organic test, abundantly inhabiting ocean and coastal sediments—and their calibration as indicator for a variety of environmental conditions in field-sampling approaches. The research projects follow two general strategic tracks: (I) a biogeochemical assessment of trace-elemental ratios in foraminiferal calcium-carbonate tests using high-resolution, micro-analytical techniques; (II) a molecular approach investigating foraminiferal environmental DNA derived from coastal sediments. <br/><br/>Papers I and II concern the calibration of the benthic foraminiferal Mn/Ca proxy for marine oxygenation conditions in modern field studies. Trace-element concentrations and distributions were measured by plasma-, laser- and synchrotron-based analyses in a high-resolution, individual-foraminifera approach, and interpreted in the context of ambient physical and chemical conditions of the water column, pore-waters and sediments (including oxygen and manganese concentrations). Investigating two coastal systems with almost permanently severely oxygen-deficient bottom-waters (Santa Barbara Basin, Paper I), and undergoing a seasonal oxygenation cycle across the low- to well-oxygenated range (Gullmar Fjord, Paper II), respectively, demonstrated the utility of the Mn/Ca proxy for indicating low-oxygen conditions specifically. Continued calibration efforts under consideration of ambient oxygenation and redox regimes may open further possibilities of quantitative oxygen reconstructions. Paper III explores the use of coastal, benthic Ba/Ca records as indicator of riverine runoff and drought on land across the years 2018 and 2019, characterised by severe heat and drought, and warm and wet conditions, respectively. Benthic Ba/Ca correlated significantly with the hydroclimate conditions, as inferred from extensive meteorological and hydrological data sets of the region, highlighting qualitative proxy potential for paleo-drought reconstructions. Based on ambient sediment and pore-water geochemistry, we discuss mediation of water-column transport and pore-water Ba cycling by Fe and Mn oxides. All three investigations of these geochemical proxies (Paper I–III) highlighted the significance of biological controls on foraminiferal TE/Ca, which are species-specific and, thus, should be a deciding factor in choosing proxy candidate species. In particular the influences of micro-habitat distribution and utilised metabolic pathways by foraminifera are discussed in detail. <br/><br/>In Paper IV foraminiferal biodiversity and assemblage responses to natural and anthropogenic environmental trends in a fjord system (Swedish west coast) are documented in a metabarcoding approach. Environmental DNA successfully tracked biodiversity and community composition changes associated with contrasting ecosystems but showed damped sensitivity to environmental variability on sub-annual time-scales. Overlaps and discrepancies between molecular and traditional, observation-based assessment techniques, as well as future trajectories to resolve uncertainties are discussed. <br/><br/>Overall, this thesis solidifies and expands the currently available proxy toolbox for reconstructions of both coastal low-oxygen, as well as terrestrial hydroclimate conditions. The findings contribute towards filling current knowledge gaps pertaining to biotic impacts on foraminifera-derived biogeochemical signals and methodological uncertainties in metabarcoding approaches and highlight the significance of implementing molecular techniques in conventional foraminiferal assemblage studies.}},
  author       = {{Brinkmann, Inda}},
  isbn         = {{978-91-87847-66-0}},
  keywords     = {{benthic foraminifera; proxy calibration; trace element geochemistry; environmental DNA; deoxygenation; drought; coastal environments}},
  language     = {{eng}},
  month        = {{09}},
  number       = {{93}},
  publisher    = {{Lund University}},
  school       = {{Lund University}},
  series       = {{LUNDQUA}},
  title        = {{Coastal signals of environmental changes: foraminifera as benthic monitors}},
  url          = {{https://lup.lub.lu.se/search/files/124061164/Thesis_Inda_Brinkmann_WEB.pdf}},
  year         = {{2022}},
}