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>

Analysis of Abundance and Origin Possibility of Planktonic Foraminifera in Sulawesi Sea

Foraminifera is very diverse and adaptive, both in its morphology and biology. It is a potential bioindicator to understand the ecological and physical conditions of the ancient and modern waters based on their distribution. It has been well confirmed that the abundance of foraminifera (as a fossil) in sediment can reflect the ocean conditions above (mixed layer to upper ocean) where it was deposited. Planktonic foraminifera however can be considered as passive particles, their movement is carried by ocean currents. In consequence, the foraminifera abundance may represent more wider ocean condition according to the ocean current pattern. This study aims to examine the role of ocean currents in the distribution of foraminifera in the Sulawesi Sea. Ten gravity core sediment samples from 73-3009 m water depth were retrieved by RV Geomarin III from the Marine Geological Institute, Indonesia. We conducted quantitative analysis, including calculation of abundance and cluster analysis. Two decades (1992-2012) of ocean current simulated data from the Hybrid Coordinate Ocean Model (HYCOM) is used in this analysis, extending from 115°E-140°E and 8°N-2°S. The result indicates that planktonic foraminifera is abundant in the Sulawesi Sea by 86.3%. There were several predominant planktonic species such as Globigerinoides ruber (22.6%), Globigerina bulloides (15.3%), and Neoglobuquadrina dutertrei (10.1%). The ocean current above the sample location is constantly moving eastward as a part of the NECC. The average currents velocity shows that foraminifera in sample site S-03 with depth 2064 m may originated from up to 1035 kilometers away from its recent location.

Roles of insolation forcing and CO2 forcing on Late Pleistocene seasonal sea surface temperatures

Late Pleistocene changes in insolation, greenhouse gas concentrations, and ice sheets have different spatially and seasonally modulated climatic fingerprints. By exploring the seasonality of paleoclimate proxy data, we gain deeper insight into the drivers of climate changes. Here, we investigate changes in alkenone-based annual mean and Globigerinoides ruber Mg/Ca-based summer sea surface temperatures in the East China Sea and their linkages to climate forcing over the past 400,000 years. During interglacial-glacial cycles, there are phase differences between annual mean and seasonal (summer and winter) temperatures, which relate to seasonal insolation changes. These phase differences are most evident during interglacials. During glacial terminations, temperature changes were strongly affected by CO2. Early temperature minima, ~20,000 years before glacial terminations, except the last glacial period, coincide with the largest temperature differences between summer and winter, and with the timing of the lowest atmospheric CO2 concentration. These findings imply the need to consider proxy seasonality and seasonal climate variability to estimate climate sensitivity.

Understanding the role of seawater vacuolisation in the biomineralisation of planktonic foraminifera using confocal microscopy

&lt;p&gt;The calcite shells of planktonic foraminfera are a key archive for palaeoceanic reconstruction and represent one of the largest sinks of carbon from the surface ocean. Therefore, understanding the biomineralisation process of these organisms, and how responsive it is to ocean acidification, is an important part of accurately predicting the carbon cycle response to past and future climate change events. To date, the majority of the direct observational evidence on which foraminifera biomineralisation models are based comes from shallow-dwelling benthic species. Whilst this has provided a large amount of important information, it is not known how applicable these models are to the low-Mg planktonic foraminifera. In particular, key questions regarding the relative importance of seawater vacuolisation (SWV) versus calcium transmembrane transport (TMT) remain unresolved. We present the results of fluorescent labelling experiments on intact, decalcified planktonic foraminifera (&lt;em&gt;Globigerinoides ruber&lt;/em&gt; and &lt;em&gt;Globigerinella siphonifera&lt;/em&gt;) using the cell-impermeable dyes calcein, FITC-dextran, and SNARF-dextran, enabling direct observation of seawater vacuoles within the cell via confocal microscopy. Our results indicate that seawater endocytosis plays a dominant role in the calcification process. Seawater vacuoles can make up a large proportion of the intracellular volume, with a residence time on the order of hours. Moreover, we show that the skeleton is labelled with fluorescent dyes such that seawater derived from these vacuoles must be present at the calcification site. Along with inferences based on geochemical data [Evans &lt;em&gt;et al&lt;/em&gt;., 2018], our results strongly argue that biomineralisation models centred on seawater endocytosis are applicable to the planktonic foraminifera.&lt;/p&gt;&lt;p&gt;Evans, D., Erez, J., M&amp;#252;ller, W. [2018] Assessing foraminifera biomineralisation models through trace element data of cultures under variable seawater chemistry. &lt;em&gt;GCA&lt;/em&gt; &lt;strong&gt;236&lt;/strong&gt;:198.&lt;/p&gt;

Unique Authigenic Mineral Assemblages and Planktonic Foraminifera Reveal Dynamic Cold Seepage in the Southern South China Sea

Many cold seeps and gas hydrate areas have not been discovered beside the Beikan basin in the southern South China Sea (SCS), and their characteristics and histories also remain poorly known. Here we describe authigenic minerals and the carbon and oxygen isotopic composition of planktonic foraminifera Globigerinoides ruber from sediment core 2PC, recovered from the gas hydrate zone of the Nansha Trough, southern SCS, to elucidate its history of dynamic cold seepage. We infer that the occurrence of authigenic gypsum crystals and pyrite concretions, and anomalously negative δ13C values of Globigerinoides ruber, reflect paleo-methane seepage. Two major methane release events were identified, based on remarkable excursions in foraminifera δ13C at depths of 150–250 cm and 350–370 cm. Euhedral gypsum crystals and tubular pyrite concretions co-occur with extremely negative planktonic foraminifera δ13C values, indicating a shift in the sulfate methane transition zone and a change in the methane flux. Our data suggest that authigenic mineral assemblages and δ13C values of planktonic foraminifera provide a valuable tool in elucidating the characteristics of dynamic methane seepage in a marine environment.

Zooplankters in an oligotrophic ocean: contrasts in the niches of the foraminifers Globigerinoides ruber and Trilobatus sacculifer in the tropical South Pacific

The distributions of two morphologically similar planktonic foraminifera (Globigerinoides ruber and Trilobus sacculifer) that are major taxa in the mixed layer of the tropical South Pacific Ocean are related to environmental variables (sea surface temperature, chlorophyll-a, nitrate, phosphate, salinity, oxygen) to determine the extent to which their niches overlap. Their distributions in ForCenS, a database of species in seafloor sediment are studied as a proxy for upper ocean data and are analysed as occurrences using MaxEnt, and as relative abundances via non-parametric regression (Random Forests). Their distributions are similar and their co-occurrences are high but relations between their abundances and the environmental variables are complex and non-linear. In the occurrence analysis sea surface temperature is the strongest predictor of niche suitability, followed by chlorophyll-a; environments between 0 – 20° S are mapped as the most suitable for both species. To the contrary, predicted species distributions are strongly differentiated by the abundance analysis. Nitrate and chlorophyll-a are primary variables in the map of predicted relative abundances of Globigerinoides ruber, with maxima in the hyper-oligotrophic zone of the subtropical gyre. In contrast, sea surface temperature and chlorophyll-a are primary variables in the map for Trilobatus sacculifer and predicted maxima are at the margins of the hyper-oligotrophic zone and near the West Pacific Warm Pool. The high relative abundance of Globigerinoides ruber in the hyper-oligotrophic zone is attributed to its close photosymbiotic relation with on-board dinoflagellates; this compensates for the low primary productivity in the zone. It is clearly identified as the best-adapted planktonic foraminifer in this huge marine ‘desert’ and might serve as a useful proxy. The photosymbiotic relation is less apparent in Trilobatus sacculifer which, as in vitro research suggests, primarily depends on particulate nutrition. The study shows the value of abundance over occurrence data for analysing the trophic resources of these zooplankters.

CHANGES IN WATER MASSES IN THE LATE QUATERNARY RECORDED AT URUGUAYAN CONTINENTAL SLOPE (SOUTH ATLANTIC OCEAN) / MUDANÇAS NAS MASSAS DE ÁGUA DURANTE O QUATERNÁRIO TARDIO REGISTADAS NO TALUDE CONTINENTAL URUGUAIO (OCEANO ATLÂNTICO SUL)

Planktonic foraminifera inhabit in the ocean waters and their spatial distribution is driven mainly by surface temperature. Thus, the tests remain deposited in the ocean sediment show different assemblages according to global climate zones. The main goal of this study was to assess the planktonic foraminifera found in the lowest continental slope of Uruguayan Continental Margin (UCM), and to identify the best criteria for future late Quaternary biostratigraphic and paleoceanographic models and based on carbonate preservation to identify water masses changes. For this purpose, this work examines foraminifera within a sediment core (T-90, 372 cm recovery, 3273 m water depth) collected in the lowest slope of UCM using a gravity corer. Forty height samples were selected along the core for foraminifera presence/absence analysis, and 13 samples, in the core section between 20 and 100 cm for foraminiferal faunal census. The age model was based on three AMS 14C dating. Foraminifera were absent in the core bottom, but were very abundant in its upper part. This variation of foraminifera was associated with fluctuations of lysocline in the glacial/interglacial transition, related to changes in geometry of bottom water masses. The most abundant species were Globorotalia inflata, Neogloboquadrina incompta, Globigerina bulloides, Globorotalia crassaformis, Globigerinoides ruber (white, sensu stricto) and Neogloboquadrina pachyderma. Principal component analysis (PCA) allowed to distinguished 3 groups of species in terms of climate zones: G. inflata (transicional), N. incompta (subpolar) and N. pachyderma (polar). Cluster analysis also identified three patterns of relative abundance among these three species, which can be related to oscillations in the latitude of Brazil-Malvinas Confluence zone during the last 15 ka. For future studies, it will be possible to check the relationship between these species as indicators of others paleoceanographic events in the study area. ResumoOs foraminíferos planctônicos habitam os oceanos sendo a sua distribuição espacial influenciada principalmente pela temperatura das águas de superfície. As suas carapaças depositadas no sedimento oceânico registam diferentes associações de acordo com as zonas climáticas globais. O principal objetivo deste trabalho é identificar mudanças de massas de água, no talude inferior da Margem Continental Uruguaia (UCM), com base na preservação de carbonatos e nas associações de foraminíferos planctônicos. Este trabalho baseia-se no estudo de foraminíferos planctônicos num testemunho de sedimentos (T-90, 372 cm de recuperação) recolhido a 3273 m de profundidade de lâmina de água, no talude continental inferior de UCM. Foram selecionadas 40 amostras ao longo do testemunho para análise presença / ausência de foraminíferos, e 13 amostras, na seção central entre 20 e 100 cm para o estudo das associações de foraminíferos. O modelo de idade foi baseado em três datações de radiocarbono por AMS. Os foraminíferos estão ausentes na extremidade inferior do testemunho, mas são muito abundantes na secção superior. Esta variação da abundância de foraminíferos poderá estar associada a flutuações da lisoclina na transição glacial/interglacial, relacionadas com mudanças na geometria das massas de água do fundo. As espécies mais abundantes ao longo do testemunho são Globorotalia inflata, Neogloboquadrina incompta, Globigerina bulloides, Globorotalia crassaformis, Globigerinoides ruber (branco, sensu stricto) e Neogloboquadrina pachyderma. A análise de componentes principais (PCA) permitiu distinguir 3 grupos de espécies em termos de zonas climáticas: G. inflata (transicional), N. incompta (subpolar) e N. pachyderma (polar). A análise de agrupamento permitiu identificar três padrões de abundância relativa entre essas três espécies, que podem estar relacionadas a oscilações na latitude da zona de confluência Brasil-Malvinas durante os últimos 15 ka. Estudos futuros, poderão basear-se na relação entre estas espécies para traçar eventos paleoceanográficos na região estudada.