Impact of large volcanic events on the marine environment recorded in marine cores

<p>Explosive silicic volcanic eruptions blanket widespread terrestrial and marine areas in ash, and have a profound effect on climate and local ecosystems. Short-term climate effects are caused by the dispersal of ash, but the injection of gas into the stratosphere, with sulphur being particularly important, drives a cooling of the climate that can last several years. These prolonged perturbations have been observed and recorded in recent decades, but despite the importance of the ocean in regulating global atmospheric climate, little is known about how and to what extent the climate signal produced by volcanic eruptions alters the oceanic environment. As the composition of foraminifera tests is highly sensitive to changes in the surrounding environment, a significant sea surface temperature decrease following a large silicic volcanic eruption may be recorded in the tests of live planktic foraminifera, now preserved in marine sediments. This study examines marine cores (and foraminifera within) that contain tephra units from three major volcanic events to determine if changes can be resolved in ocean temperature and/or foraminifera test morphology following large silicic eruptions. The Holocene Taupo, Waimihia and Mamaku tephra units have been identified in a series of marine sediment cores collected from areas with high sedimentation rates off the east coast of North Island, New Zealand. The sources of these eruptions were from two calderas within the Taupo Volcanic Zone, one of the most active and important rhyolitic regions in the world. Sampling of sediment and foraminifera from these cores has been undertaken at 0.5 cm intervals above and below each tephra. This equates to varying sampling resolutions between cores of 5-30 years, with sufficient sampling taken to establish a stratigraphic record of >100 years either side of each tephra unit. A detailed stratigraphy was undertaken on the sediment surrounding all tephra units, including grain size and CaCO₃ analyses, to identify primary and secondary tephra deposits. One core, Tan0810-12 that contained solely Taupo tephra, was selected for foraminiferal analyses to determine changes in ocean temperature and foraminifera test morphology following this eruption. This core was selected based on the results of the stratigraphic analyses that identified the tephra as a primary deposit with minimal bioturbation above the ash layer and a very high sedimentation rate that enabled sub-decadal scale sampling. Scanning electron microscope imaging was employed to identify the presence of surface contaminants on and within the foraminifera tests and allowed observations of test morphology and size. The morphologies of planktic foraminifera species Globigerinoides ruber and Globigerina bulloides showed no obvious change following the Taupo eruption. The Globigerinoides ruber test sizes distinctly decreased for a period after the eruption, while Globigerina bulloides tests slightly increased in size, correlating well with a decrease in sea surface temperature after the eruption as these species prefer warmer and colder temperatures, respectively. This suggests there is potential for test size to be employed as a proxy for temperature change in conjunction with geochemical analyses. Mg/Ca temperature analyses were conducted in situ using laser ablation inductively coupled plasma mass spectrometry. Both species indicated a decrease in sea surface temperatures when comparing results from tests collected below the tephra deposit to those above. Further results indicate ocean temperature may not have recovered for more than 65 years after the eruption. Such a rapid change in the oceanic environment not only has drastic implications for marine ecosystems but also atmospheric climate, and therefore, terrestrial ecosystems. To reduce the margin of error and determine a more exact value of temperature change following the eruption a greater population of foraminifera is needed. Nonetheless, this study highlights the potential of this method in determining how the oceans are impacted by volcanism and how further research is needed to determine the effects of volcanic eruptions on past and future climate.</p>

Impact of large volcanic events on the marine environment recorded in marine cores

<p>Explosive silicic volcanic eruptions blanket widespread terrestrial and marine areas in ash, and have a profound effect on climate and local ecosystems. Short-term climate effects are caused by the dispersal of ash, but the injection of gas into the stratosphere, with sulphur being particularly important, drives a cooling of the climate that can last several years. These prolonged perturbations have been observed and recorded in recent decades, but despite the importance of the ocean in regulating global atmospheric climate, little is known about how and to what extent the climate signal produced by volcanic eruptions alters the oceanic environment. As the composition of foraminifera tests is highly sensitive to changes in the surrounding environment, a significant sea surface temperature decrease following a large silicic volcanic eruption may be recorded in the tests of live planktic foraminifera, now preserved in marine sediments. This study examines marine cores (and foraminifera within) that contain tephra units from three major volcanic events to determine if changes can be resolved in ocean temperature and/or foraminifera test morphology following large silicic eruptions. The Holocene Taupo, Waimihia and Mamaku tephra units have been identified in a series of marine sediment cores collected from areas with high sedimentation rates off the east coast of North Island, New Zealand. The sources of these eruptions were from two calderas within the Taupo Volcanic Zone, one of the most active and important rhyolitic regions in the world. Sampling of sediment and foraminifera from these cores has been undertaken at 0.5 cm intervals above and below each tephra. This equates to varying sampling resolutions between cores of 5-30 years, with sufficient sampling taken to establish a stratigraphic record of >100 years either side of each tephra unit. A detailed stratigraphy was undertaken on the sediment surrounding all tephra units, including grain size and CaCO₃ analyses, to identify primary and secondary tephra deposits. One core, Tan0810-12 that contained solely Taupo tephra, was selected for foraminiferal analyses to determine changes in ocean temperature and foraminifera test morphology following this eruption. This core was selected based on the results of the stratigraphic analyses that identified the tephra as a primary deposit with minimal bioturbation above the ash layer and a very high sedimentation rate that enabled sub-decadal scale sampling. Scanning electron microscope imaging was employed to identify the presence of surface contaminants on and within the foraminifera tests and allowed observations of test morphology and size. The morphologies of planktic foraminifera species Globigerinoides ruber and Globigerina bulloides showed no obvious change following the Taupo eruption. The Globigerinoides ruber test sizes distinctly decreased for a period after the eruption, while Globigerina bulloides tests slightly increased in size, correlating well with a decrease in sea surface temperature after the eruption as these species prefer warmer and colder temperatures, respectively. This suggests there is potential for test size to be employed as a proxy for temperature change in conjunction with geochemical analyses. Mg/Ca temperature analyses were conducted in situ using laser ablation inductively coupled plasma mass spectrometry. Both species indicated a decrease in sea surface temperatures when comparing results from tests collected below the tephra deposit to those above. Further results indicate ocean temperature may not have recovered for more than 65 years after the eruption. Such a rapid change in the oceanic environment not only has drastic implications for marine ecosystems but also atmospheric climate, and therefore, terrestrial ecosystems. To reduce the margin of error and determine a more exact value of temperature change following the eruption a greater population of foraminifera is needed. Nonetheless, this study highlights the potential of this method in determining how the oceans are impacted by volcanism and how further research is needed to determine the effects of volcanic eruptions on past and future climate.</p>

Ecological, Oceanographic and Temperature Controls on the Incorporation of Trace Elements into Globigerina Bulloides and Globoconella Inflata in the Southwest Pacific Ocean

<p>Trace element ratios (Mg/Ca, Al/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca) measured by laser ablation inductively coupled plasma mass spectrometry plus and test weight and size data are presented for two planktonic foraminiferal species, Globigerina bulloides and Globoconella inflata. These data will be used to investigate the potential of Mg/Ca ocean thermometry and other trace element proxies of past ocean chemistry using these species. Foraminifera were sampled from core-top sediments from 10 sites in the Southwest Pacific Ocean, east of New Zealand, spanning latitudes of c.33' to 54' S and temperatures of 6-19' C at 75-300 m water depth. Mg/Ca in G. bulloides correlates strongly with observed water temperatures at 200 m depth and yields a new calibration of Mg/Ca = 0.941 exp 0.0693*T (r2 = 0.95). When G. bulloides Mg/Ca data from this study are combined with previously published data for this species, a calibration of Mg/Ca = 0.998 exp 0.066*T (r2 = 0.97) is defined. Significant variability of Mg/Ca values (20-30%) was found for the four largest chambers of G. bulloides with the final chamber consistently recording the lowest Mg/Ca values. This is interpreted to reflect changes in the depth habitat towards the end of the life cycle of G. bulloides. Levels of A1 and the micronutrients Mn and Zn in G. bulloides were found to differ significantly between Subtropical and Subantarctic Water masses, suggesting these elements can potentially be used as water mass tracers. No clear relationship between Mg/Ca and temperature was observed for G.inflata. This is interpreted, in part, to reflect the ecological niche that G. inflata occupies at the base of the thermocline, coupled with the impact of heavy secondary calcite which lowers Mg/Ca values. A correlation between size normalized test weight, water temperature and seawater carbonate ion concentration is observed for G. bulloides suggesting a modern calibration that could be potentially applied for paleoceanographic reconstructions of ocean water temperature and carbonate ion concentrations. No correlation between temperature or carbonate ion was found with size normalized G. inflata test weights. However, a bimodal population of G. inflata test weights indicates a possible link between high levels of chlorophyll-a in surface waters and light G. inflata tests. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and solution-based techniques for measuring Mg/Ca in G. bulloides yield compatible results. However, this is possible only when minimal dissolution of test calcite has occurred during the reductive and dilute acid leaching stages of cleaning prior to solution analysis, or, if only the older three visible chambers are used for LA-ICP-MS analysis. LA-ICP-MS analysis is an effective method for measuring trace element/Ca values in foraminifera, especially for small sample sizes, and enables the test to be used for further geochemical analysis (e.g. boron or carbon/oxygen stable isotope analysis).</p>

Ecological, Oceanographic and Temperature Controls on the Incorporation of Trace Elements into Globigerina Bulloides and Globoconella Inflata in the Southwest Pacific Ocean

<p>Trace element ratios (Mg/Ca, Al/Ca, Mn/Ca, Zn/Ca, Sr/Ca, Ba/Ca) measured by laser ablation inductively coupled plasma mass spectrometry plus and test weight and size data are presented for two planktonic foraminiferal species, Globigerina bulloides and Globoconella inflata. These data will be used to investigate the potential of Mg/Ca ocean thermometry and other trace element proxies of past ocean chemistry using these species. Foraminifera were sampled from core-top sediments from 10 sites in the Southwest Pacific Ocean, east of New Zealand, spanning latitudes of c.33' to 54' S and temperatures of 6-19' C at 75-300 m water depth. Mg/Ca in G. bulloides correlates strongly with observed water temperatures at 200 m depth and yields a new calibration of Mg/Ca = 0.941 exp 0.0693*T (r2 = 0.95). When G. bulloides Mg/Ca data from this study are combined with previously published data for this species, a calibration of Mg/Ca = 0.998 exp 0.066*T (r2 = 0.97) is defined. Significant variability of Mg/Ca values (20-30%) was found for the four largest chambers of G. bulloides with the final chamber consistently recording the lowest Mg/Ca values. This is interpreted to reflect changes in the depth habitat towards the end of the life cycle of G. bulloides. Levels of A1 and the micronutrients Mn and Zn in G. bulloides were found to differ significantly between Subtropical and Subantarctic Water masses, suggesting these elements can potentially be used as water mass tracers. No clear relationship between Mg/Ca and temperature was observed for G.inflata. This is interpreted, in part, to reflect the ecological niche that G. inflata occupies at the base of the thermocline, coupled with the impact of heavy secondary calcite which lowers Mg/Ca values. A correlation between size normalized test weight, water temperature and seawater carbonate ion concentration is observed for G. bulloides suggesting a modern calibration that could be potentially applied for paleoceanographic reconstructions of ocean water temperature and carbonate ion concentrations. No correlation between temperature or carbonate ion was found with size normalized G. inflata test weights. However, a bimodal population of G. inflata test weights indicates a possible link between high levels of chlorophyll-a in surface waters and light G. inflata tests. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) and solution-based techniques for measuring Mg/Ca in G. bulloides yield compatible results. However, this is possible only when minimal dissolution of test calcite has occurred during the reductive and dilute acid leaching stages of cleaning prior to solution analysis, or, if only the older three visible chambers are used for LA-ICP-MS analysis. LA-ICP-MS analysis is an effective method for measuring trace element/Ca values in foraminifera, especially for small sample sizes, and enables the test to be used for further geochemical analysis (e.g. boron or carbon/oxygen stable isotope analysis).</p>

Late Pliocene to Early Pleistocene Planktonic Foraminifera from Northern Indian Ocean (Andaman and Nicobar Islands): Interpretation on Cooling Event and Ocean Upwelling

ABSTRACT Thirty-two planktonic foraminiferal taxa have been identified based on Bright Field microscopic study as well as Scanning Electron Microscopy on the samples collected from the outcrop adjacent to the type section of Neill West Coast Formation at Neil Island of Ritchie's Archipelago, northern Indian Ocean. The planktonic foraminiferal taxa belong to ten genera viz., Dentoglobigerina, Globigerina, Globigerinoides, Globoconella, Globorotalia, Globorotaloides, Globoturborotalita, Neogloboquadrina, Orbulina, and Trilobatus. A number of statistical analyses have been done in addition to taxonomic study to interpret the palaeocenographic scenario. We performed PCA analysis on the foraminiferal content of the samples to test the relatedness. Two biozones have been established by Stratigraphically Constrained Cluster Analysis (CONISS). We used SHEBI (SHE analysis for biozone identification) analysis to precisely demarcate seven biozones. Attempts have been made to decipher the Plio–Pleistocene boundary in the Neill West Coast Formation based on specific zonal markers. The presence of some taxa (e.g., Globoconella inflata, Globigerina bulloides, and Neogloboquadrina pachyderma) indicates the initiation of a cooling event from late Pliocene onwards. An event of ocean upwelling also has been identified based on the presence of Globigerina bulloides, Neogloboquadrina pachyderma, and N. dutertrei from the late Pliocene to early Pleistocene of the northern Indian Ocean that also correlates with palaeoceanographic records known from other upwelling regions.

Planktic Foraminifera changes in the western Mediterranean Anthropocene

&lt;p&gt;The increase in anthropogenic induced warming over the last two centuries is impacting marine environments. Marine planktic calcifying organisms interact sensitively to changes in sea surface temperatures (SST), and the food web structure. Here, we study two high resolution multicore records from two western Mediterranean Sea regions (Alboran and Balearic basins), areas highly affected by both natural climate change and anthropogenic warming. Cores cover the time interval from the Medieval Climate Anomaly (MCA) to present. Reconstructed SSTs are in good agreement with other results, tracing temperature changes through the Common Era, and show a clear 20&lt;sup&gt;th&lt;/sup&gt; century warming signal. Both cores show opposite abundance fluctuations of planktic foraminiferal species (Globigerina bulloides, Globorotalia inflata and Globorotalia truncatulinoides) a common group of marine calcifying zooplankton. The abundance ratios between these species show the switch between winter / spring surface productivity and deep winter mixing in the Balearic basin. In the Alboran Sea, Globigerina bulloides and Globorotalia inflata instead respond to local upwelling dynamics. In the pre-industrial era, changes in planktic foraminiferal productivity and species composition can be explained mainly by the natural variability of North Atlantic Oscillation (NAO), and, to lesser extent, by the Atlantic Multidecadal Oscillation (AMO). In the industrial era, starting from about 1800 Common Era (CE), this variability is affected by anthropogenic surface warming, leading to enhanced vertical stratification of the upper water column, and resulting in a decrease of surface productivity at both sites. We found that natural planktic foraminiferal population dynamics in the western Mediterranean is already altered by enhanced anthropogenic impact in the industrial era, suggesting that in this region natural cycles and influences are being overprinted by human influences.&lt;/p&gt;

X-ray tomographic data of planktonic foraminifera species Globigerina bulloides from the Eastern Tropical Atlantic across Termination II

Increased planktonic foraminifera shell weights were recorded during the course of Termination II at a tropical site off the shore of the Mauritanian coast. In order to investigate these increased shell mass values, a series of physicochemical analyses were performed, including X-ray computed tomography (CT). The data are given here. Furthermore, the relevant CT setup, scanning, reconstruction, and visualization methods are explained and the acquired datasets are given, together with 3D volumes and models of the scanned specimens.

Evidence of Stable Foraminifera Biomineralization during the Last Two Climate Cycles in the Tropical Atlantic Ocean

Planktonic foraminiferal biomineralization intensity, reflected by the weight of their shell calcite mass, affects global carbonate deposition and is known to follow climatic cycles by being increased during glacial stages and decreased during interglacial stages. Here, we measure the dissolution state and the mass of the shells of the planktonic foraminifera species Globigerina bulloides from a Tropical Eastern North Atlantic site over the last two glacial–interglacial climatic transitions, and we report no major changes in plankton calcite production with the atmospheric pCO2 variations. We attribute this consistency in foraminifera calcification to the climatic and hydrological stability of the tropical regions. However, we recorded increased shell masses midway through the penultimate deglaciation (Termination II). In order to elucidate the cause of the increased shell weights, we performed δ18O, Mg/Ca, and μCT measurements on the same shells from a number of samples surrounding this event. Compared with the lighter ones, we find that the foraminifera of increased weight are internally contaminated by sediment infilling and that their shell masses respond to local surface seawater density changes.

Evidence of Stable Foraminifera Biomineralization During the Last Two Climate Cycles in the Tropical Atlantic Ocean

Planktonic foraminiferal biomineralization intensity, reflected by their shell calcite mass, affects global carbonate deposition and is known to follow the climate cycles by being increased during glacial stages and decreased during interglacial ones. Here we measure the dissolution state and the mass of the shells of the planktonic foraminifera species Globigerina bulloides from a Tropical Eastern North Atlantic site over the last two glacial-interglacial climatic transitions and we report no major changes in plankton calcite production with the atmospheric pCO2 variations. We attribute this consistency in foraminifera calcification to the climatic and hydrological stability of the tropical regions. We however recorded increased shell masses midway through the penultimate deglaciation (Termination II). In order to elucidate the cause of the increased shell weights we performed &delta;18O, Mg/Ca and &mu;CT measurements on the same shells from a number of samples surrounding this event. We find that shells of increased mass are internally contaminated by sediment infilling and that shell weights are responding to local hydrographic changes.

X-ray tomographic data of planktonic foraminifera species Globigerina bulloides from the Eastern Tropical Atlantic across Termination II

Elevated shell weights of the planktonic foraminifera species Globigerina bulloides were recorded during the course of Termination II at a tropical site offshore the Mauritanian coast. In order to investigate these increased shell mass values a series of physicochemical analyses were performed including X-ray computed tomography (CT) and the data are reported here. Furthermore, the relevant CT setup, scanning, reconstructing, and visualization methods are explained and the acquired datasets are given together with 3D volumes and models of the scanned specimens.