8 research outputs found
An expanded database of Southern Hemisphere surface sediment dinoflagellate cyst assemblages and their oceanographic affinities
Dinoflagellate cyst assemblages present a valuable proxy to infer paleoceanographic conditions, yet factors influencing geographic distributions of species remain largely unknown, especially in the Southern Ocean. Strong lateral transport, sea-ice dynamics, and a sparse and uneven geographic distribution of surface sediment samples have limited the use of dinocyst assemblages as a quantitative proxy for paleo-environmental conditions such as sea surface temperature (SST), nutrient concentrations, salinity, and sea ice (presence). In this study we present a new set of surface sediment samples (nCombining double low line66) from around Antarctica, doubling the number of Antarctic-proximal samples to 100 (dataset wsi_100) and increasing the total number of Southern Hemisphere samples to 655 (dataset sh_655). Additionally, we use modelled ocean conditions and apply Lagrangian techniques to all Southern Hemisphere sample stations to quantify and evaluate the influence of lateral transport on the sinking trajectory of microplankton and, with that, to the inferred ocean conditions. k-means cluster analysis on the wsi_100 dataset demonstrates the strong affinity of Selenopemphix antarctica with sea-ice presence and of Islandinium spp. with low-salinity conditions. For the entire Southern Hemisphere, the k-means cluster analysis identifies nine clusters with a characteristic assemblage. In most clusters a single dinocyst species dominates the assemblage. These clusters correspond to well-defined oceanic conditions in specific Southern Ocean zones or along the ocean fronts. We find that, when lateral transport is predominantly zonal, the environmental parameters inferred from the sea floor assemblages mostly correspond to those of the overlying ocean surface. In this case, the transport factor can thus be neglected and will not represent a bias in the reconstructions. Yet, for some individual sites, e.g. deep-water sites or sites under strong-current regimes, lateral transport can play a large role. The results of our study further constrain environmental conditions represented by dinocyst assemblages and the location of Southern Ocean frontal systems
There and back again: The journey of sinking marine microplankton and its implication for past, present and future climate
Anthropogenic climate change is one of the greatest challenges for humanity today. How does the Earth system react to the atmospheric greenhouse gas increase that has never happened before with such speed in Earth's history?
So far, climate models project an increase of the global average temperature, sea level and the number of `extremely' warm days in the coming decades and centuries. Although it is clear that the Earth is warming, uncertainty remains in the progression of those developments.
These climate models are inherently wrong, but are they useful? Climate models give a proper representation of present-day climate, which we know from validations with observations.
These models, which contain fundamental physical processes and have been developed over the past decades, cannot be validated in the increased greenhouse-climate of the future. We can however, compare the models with observations of warmer climates in the past, which are similar to the future climate, to get an understanding of these type of `extreme' climates.
Although (unfortunately) no direct observations are available for the past hundred millions of years, we do find indirect evidence about the past climate (for example fossils or ice cores). These so-called proxies provide an archive of past climate and can be used to compare with climate model simulations. As a result, the combination of models and proxies of past climate can be used to get a better understanding of how a future climate, which is warmer than today, may look like.
A primary part of the Earth's archive to reconstruct past climates is provided by marine sediments, consisting of (fossil remains from) microplankton. The microplankton species in the bottom sediments originated from a location close to the ocean surface before they started sinking to the bottom. Hence, microplankton at the ocean bottom is representative of the ocean surface environment. It is often assumed that these planktonic species sunk vertically downwards. However, the microplankton is transported laterally by ocean currents during its sinking journey.
In this thesis, we investigate how sedimentary distributions of microplankton can be explained. We determine how sinking microplankton is advected by ocean currents, which may have great implications for the interpretation of sedimentary microplankton data. For example, subtropical and (sub)polar microplankton species alternate in sediment cores near Antarctica from 34 million years ago until the present-day. If subtropical microplankton species are found near Antarctica in a specific time period, two hypotheses can be tested: (a) Antarctica had a subtropical climate, or (b) Antarctica was not subtropical, but the microplankton were transported laterally by ocean currents and originated from another region with a subtropical climate.
We study microplankton particles at the ocean bottom, which got there after a sinking journey, and determine their origin at the ocean surface back again.
The ultimate goal is to bridge a gap between the models, which represent the global climate, and the measurements, representing the climate at specific geographic locations. As such, we study past climates back again, to get an idea how we get there in the future
There and back again: The journey of sinking marine microplankton and its implication for past, present and future climate
Anthropogenic climate change is one of the greatest challenges for humanity today. How does the Earth system react to the atmospheric greenhouse gas increase that has never happened before with such speed in Earth's history?
So far, climate models project an increase of the global average temperature, sea level and the number of `extremely' warm days in the coming decades and centuries. Although it is clear that the Earth is warming, uncertainty remains in the progression of those developments.
These climate models are inherently wrong, but are they useful? Climate models give a proper representation of present-day climate, which we know from validations with observations.
These models, which contain fundamental physical processes and have been developed over the past decades, cannot be validated in the increased greenhouse-climate of the future. We can however, compare the models with observations of warmer climates in the past, which are similar to the future climate, to get an understanding of these type of `extreme' climates.
Although (unfortunately) no direct observations are available for the past hundred millions of years, we do find indirect evidence about the past climate (for example fossils or ice cores). These so-called proxies provide an archive of past climate and can be used to compare with climate model simulations. As a result, the combination of models and proxies of past climate can be used to get a better understanding of how a future climate, which is warmer than today, may look like.
A primary part of the Earth's archive to reconstruct past climates is provided by marine sediments, consisting of (fossil remains from) microplankton. The microplankton species in the bottom sediments originated from a location close to the ocean surface before they started sinking to the bottom. Hence, microplankton at the ocean bottom is representative of the ocean surface environment. It is often assumed that these planktonic species sunk vertically downwards. However, the microplankton is transported laterally by ocean currents during its sinking journey.
In this thesis, we investigate how sedimentary distributions of microplankton can be explained. We determine how sinking microplankton is advected by ocean currents, which may have great implications for the interpretation of sedimentary microplankton data. For example, subtropical and (sub)polar microplankton species alternate in sediment cores near Antarctica from 34 million years ago until the present-day. If subtropical microplankton species are found near Antarctica in a specific time period, two hypotheses can be tested: (a) Antarctica had a subtropical climate, or (b) Antarctica was not subtropical, but the microplankton were transported laterally by ocean currents and originated from another region with a subtropical climate.
We study microplankton particles at the ocean bottom, which got there after a sinking journey, and determine their origin at the ocean surface back again.
The ultimate goal is to bridge a gap between the models, which represent the global climate, and the measurements, representing the climate at specific geographic locations. As such, we study past climates back again, to get an idea how we get there in the future
Limited lateral transport bias during export of sea surface temperature proxy carriers in the Mediterranean Sea
Some lipid-biomarker-based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the UK’37 and TEX86 paleothermometers, respectively. We use a simple 30-day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md−1). For the assessed scenarios, lateral transport bias is generally small (always <0.85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in UK’37- or TEX86-based SSTs
Limited lateral transport bias during export of sea surface temperature proxy carriers in the Mediterranean Sea
Some lipid-biomarker-based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the UK’37 and TEX86 paleothermometers, respectively. We use a simple 30-day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md−1). For the assessed scenarios, lateral transport bias is generally small (always <0.85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in UK’37- or TEX86-based SSTs
Limited lateral transport bias during export of sea surface temperature proxy carriers in the Mediterranean Sea
Some lipid-biomarker-based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the UK’37 and TEX86 paleothermometers, respectively. We use a simple 30-day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md−1). For the assessed scenarios, lateral transport bias is generally small (always <0.85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in UK’37- or TEX86-based SSTs
Limited lateral transport bias during export of sea surface temperature proxy carriers in the Mediterranean Sea
Some lipid-biomarker-based sea surface temperature (SST) proxies applied in the modern Mediterranean Sea exhibit large offsets from expected values, generating uncertainties in climate reconstructions. Lateral transport of proxy carriers along ocean currents prior to burial can contribute to this offset between reconstructed and expected SSTs. We perform virtual particle tracking experiments to simulate transport prior to and during sinking and derive a quantitative estimate of transport bias for alkenones and glycerol dibiphytanyl glycerol tetraethers (GDGTs), which form the basis of the UK’37 and TEX86 paleothermometers, respectively. We use a simple 30-day surface advection scenario and sinking speeds appropriate for the export of various proxy carriers (6, 12, 25, 50, 100, 250, 500, and 1000 md−1). For the assessed scenarios, lateral transport bias is generally small (always <0.85°C) within the Mediterranean Sea and does not substantially contribute to uncertainties in UK’37- or TEX86-based SSTs