1,721,097 research outputs found
Instrumental validation of Globigerinoides ruber Mg/Ca as a proxy for NE Pacific summer SST
Full text linkAccurate reconstruction of sea surface temperature (SST) is a high research priority, given that it is such a crucial variable in the Earth’s climate system. The Mg/Ca composition of Globigerinoides ruber (white) has been calibrated and applied for a number of tropical and extratropical paleo?SST reconstructions, though validation studies of the proxy against instrumental observations are relatively scarce. Here we present a validation of G. ruber Mg/Ca?derived SSTs against instrumental summer values, firstly from the modern seasonal water column perspective, and secondly from a 20th century observational time series. The study occurs in the San Lázaro Basin (SLB), one of the marginal basins in the NE Pacific known for very high sedimentation rates, excellent preservation, laminated sequences, and the ability to record upwelling processes on high?resolution timescales, from interannual climatic variability (El Niño / Southern Oscillation (ENSO)) to interdecadal (e.g., the Pacific Decadal Oscillation (PDO)). Results suggest that the proxy best reflects the summer season. The proxy?instrument time?series comparison for summer SSTs displays remarkable agreement, driven largely by ENSO cycles for the past century, with some events missing due to scarcity of foraminiferal specimens and/or lack of sufficient temporal resolution. This study validates the G. ruber Mg/Ca proxy for summer SSTs in this region, and suggests its high fidelity to reconstruct summer SST from SLB over longer timescales to record multi?decadal and multi?centennial variabilities
Multi-species planktonic foraminiferal Mg/Ca and δ18O as recorders of surface ocean paleoclimatic processes : 2 case studies from diverse oceanographic regions and timescales
Full text linkDurante procesos de calcificación los foraminíferos planctónicos incorporan Mg/Ca y fraccionan los isótopos de oxígeno (δ18O) en sus cáscaras dependiendo de la temperatura, y de la temperatura-δ18O de la masa de agua (δ18OSW) donde calcifican, respectivamente. Medidas de Mg/Ca-δ18O en foraminíferos planctónicos han sido ampliamente utilizadas para reconstruir cambios de temperatura y derivar δ18OSW (corregido por el volumen de hielo; δ18OSW-IVC) como proxy de salinidad. Esta tesis utiliza nuevas reconstrucciones de Mg/Ca-temperatura y δ18OSW-IVC para entender cambios en la estructura de la columna de agua durante la Transición del Pleistoceno Medio (MPT; 1250-700 ka) y la Terminación 1 (T1)-Holoceno temprano (20-3 ka) en el Océano Austral y Océano Pacífico, respectivamente. Aunque escalas de tiempos diferentes, ambos fueron períodos de cambios climáticos importantes y entender sus causas es importante para establecer factores que originan la variabilidad natural del clima. La combinación de procesos físicos y biogeoquímicos en el Océano Austral regulan el intercambio de CO2 entre el océano y la atmósfera durante ciclos glaciales-interglaciales. Reconstrucciones de Mg/Ca-temperatura y δ18OSW-IVC basados en Neogloquadrina pachyderma (sinistral) en la Zona Subantárctica (ODP Site 1090) muestran que al comienzo del MPT (̃1250 ka), la expansión de los frentes polares Antárcticos originó el enfriamiento glacial y reducción de salinidad de la superficie del Océano Austral. Se propone que estos cambios conllevaron a la estratificación de la superficie de este océano durante glaciaciones, evitando el intercambio de CO2 con la atmósfera y por lo tanto incrementando el almacenamiento de carbono (C) en profundidad en las glaciaciones siguientes. Adicionalmente se estudió la influencia de la expansión de los frentes polares en la estructura de la columna de agua de la Zona Subantárctica mediante la comparación de registros de Mg/Ca-temperatura y δ18OSW-IVC de foraminíferas planctónicos con profundidades de hábitat distintos; Globigerina bulloides (superficie), N. pachyderma (subsuperficie), and Globorotalii crassaformis (thermoclina). Estos resultados sugieren que la termoclina/haloclina de esa zona se hizo más somera entre 1500-1300 ka probablemente incrementando la disponibilidad de macro-nutrientes en la superficie de la zona. Esto, aunado a la fertilización por Fe durante las glaciaciones del MPT, eventualmente permitió el aumento de productividad observado en la zona, lo cual junto con la estratificación del Océano Austral posiblemente, pudo ocasionar la reducción glacial de pCO2 (̃30 ppm) a ̃1250 ka. Las condiciones hidrográficas de la parte superficial de la columna de agua fueron también estudiadas Corriente de California (CC, MD02-2505) durante la T1. Se ha sugerido que la formación de aguas profundas en el Atlántico Norte durante el Younger Dryas (YD) y stadial-H1 menguó, incrementando el transporte de calor y salinidad al Océano Austral. Sin embargo sus consecuencias en el Océano Pacífico aún no están bien establecidas. Aquí, reconstrucciones de Mg/Ca-temperatura y δ18OSW-IVC utilizando los morfotipos de Globigerinoides ruber white en el MD02-2505 muestran el calentamiento relativo de la zona debido al debilitamiento de la CC durante la T1 concordando el perfil de δ18OSW-IVC que sugiere condiciones menos salinas hacia el Holoceno. Incrementos pronunciados de δ18OSW-IVC (̃0.7‰) durante YD y stadial-H1 aparentemente son consecuencia de un efecto combinado del debilitamiento de la CC y la advección de aguas relativamente más salinas en el Pacífico durante YD y stadial-H1 en respuesta a los cambios en el Atlántico Norte. Este trabajo enfatiza la respuesta e importancia de las condiciones superficiales de la columna de agua en el sistema climático. En base a reconstrucciones de temperatura y salinidad superficiales se han sugerido mecanismos plausibles de la influencia de las condiciones hidrográficas del Océano Austral en el intercambio de C con la atmósfera durante el MPT y en la respuesta del Océano Pacífico a cambios en el Atlántico Norte durante la T1.During the calcification process planktonic foraminifera incorporate Mg/Ca and fractionate oxygen isotopes (δ18O) in their shells depending on the water mass' temperature and temperature-seawater δ18O composition (δ18OSW), respectively, where they calcified. Paired Mg/Ca-δ18O measurements in planktonic foraminifera have been widely used as a powerful tool to reconstruct ocean temperature and salinity changes, the latter by deconvolving ice volume corrected δ18OSW (δ18OSW-IVC). This thesis builds on new planktonic foraminiferal Mg/Ca-temperature and δ18OSW-IVC records as proxies to understand past changes in the structure of the water column during the Middle Pleistocene Transition (MPT; 1250-700 ka) and Termination 1 (T1)-early Holocene (20 to 3 ka) focusing on two regions, the Southern Ocean and North-East Pacific Ocean respectively. Although very different timescales, the MPT and T1 were two periods of important climatic changes, the causes and internal feedbacks surrounding's which are of special interest to assess the drivers of the natural climate variability. A combination of physical and biogeochemical processes in the Southern Ocean regulates the partitioning of CO2 between the ocean and the atmosphere on glacial-interglacial timescales. Neogloquadrina pachyderma (sinistral) Mg/Ca-temperature and δ18OSW-IVC records from a core located in the Subantarctic Zone (ODP Site 1090) have shown that at ~1250 ka, the onset of the MPT, the seaward expansion of the Antarctic ice sheets promoted glacial cooling and freshening of the surface Southern Ocean. We suggest that the glacial freshening could have induced Southern Ocean upper water column stratification and hence hindered the outgassing of respired CO2 to the atmosphere, increasing the storage of C at depth during glacial periods. We further explored changes in the water column structure induced by the expansion of the Antarctic polar fronts by exploiting the different depth habitat preferences of Globigerina bulloides (surface), N. pachyderma (subsurface), and Globorotalii crassaformis (thermocline). Their Mg/Ca-temperature and δ18OSW-IVC reconstructions suggested that the thermocline and halocline of the Subantarctic Zone shoaled from 1500-1300 ka, and persisted as such across the MPT, likely improving macro-nutrient availability in the surface waters. This, in combination with glacial Fe-fertilization, probably allowed the spike in productivity observed during glacial stages in and after the transition. This together with Southern Ocean stratification contributed to the glacial 30 ppm MPT drop in pCO2. The influence of past upper ocean hydrographical changes in the climate system was further studied in a core located in the southern California Current (CC, MD02-2505) across T1. Declining deep water formation in the North Atlantic during Younger Dryas (YD) and stadial-H1 resulted in an increase of heat and salinity transport to the Southern Ocean; however the response of the Pacific Ocean to those changes remains elusive. Mg/Ca-temperature reconstructions inferred from Globigerinoides ruber white morphotypes suggest that the CC weakened across T1, allowing a relative warming of the CC at ~25ºN compared to northern positions. This is further supported by δ18OSW-IVC changes toward fresher conditions into the Holocene. Increases of δ18OSW-IVC (~0.7‰) in tandem with YD and stadial-H1 are suggested to reflect the combined effect of the weakening of the fresh CC and advection of relatively salty water masses to the core in response to the North Atlantic freshening and oceanic reorganization. Overall, this work highlights the role of the upper ocean's physical properties in the Earth's climate. Based on temperature and salinity proxy reconstructions we provide plausible mechanisms to explain the role of the Southern Ocean hydrographical conditions in the storage/release of carbon at/from depth during the MPT as well as new insights on the response of the Pacific Ocean to decreases of heat and salinity transport to the North Atlantic within the last period of natural global warming
Field-based validation of a diagenetic effect on G. ruber Mg/Ca paleothermometry: Core top results from the Aegean Sea (eastern Mediterranean)
Full text linkRecent work across the Mediterranean Sea has illustrated the salinity and overgrowth effects on planktonic foraminiferal Mg/Ca, which potentially confound the use of this as a temperature proxy for paleoceanographic reconstructions. To test and verify these effects, we present new Aegean Sea results which reveal Mg/Ca values that were unreasonably high to be explained by temperature or salinity variations alone, confirming that foraminiferal Mg/Ca is affected by diagenesis. We have specifically targeted Globigerinoides ruber (w, sensu stricto), from a series of modern core tops spanning a strong sea surface salinity gradient and a minor sea surface temperature range, along a north?south Aegean Sea transect. Scanning Electron Microscopy analyses show that G. ruber specimens were covered by microscale euhedral crystallites of inorganic precipitates. This secondary calcite phase seems to be responsible for the anomalously high Mg/Ca ratios and likely formed near the sediment/water interface from CaCO3 supersaturated interstitial seawater. We also have clear evidence of diagenetic alteration in a north?south direction along the Aegean Sea, possibly depending on salinity and calcite saturation state gradients. These observations illustrate the necessity of alternative techniques (e.g., flow?through time resolved analysis or laser ablation inductively coupled plasma mass spectrometry) to potentially overcome these diagenetic issues and develop a more reliable and sensitive temperature proxy in similar subtropical settings characterized by high salinity, excessive evaporation, and restricted circulation
Derived Particulate Inorganic Carbon (PIC) and Particulate Organic Carbon (POC) ratio from ODP Site 202-1238
No full textWe estimated E. huxleyi particulate inorganic to organic carbon ratio (PIC:POC) in order to detect changes in the carbonate counter-pump to carbon pump activity, which can act as either a positive or negative feedback to atmospheric CO2 modulating air-sea gas exchange
Calcareous nannofossil assemblage data (%) from ODP Site 202-1238
No full textCoccoliths relative abundances (%) were analyzed spanning the last 30 ky at Site ODP 1238 (1°52.310′S, 82°46.934′W; 2203 m; 2203 m) in the EEP
Relative abundance of coccolithophore species in sediment core MedSeA-S7 retrieved from the Strait of Sicily during the MedSeA Cruise 2013
No full textRelative abundance of coccolithophore species in MedSeA-S7 sediment core, spanning from 1810 to 2010 years of the Common Era, examined under a polarized microscope at 1000x magnification (size fraction <63 um) at least 500 speciments were counted and identified
Relative abundance of coccolithophore species in sediment core MedSeA-S3 retrieved from the Alboran Sea during the MedSeA Cruise 2013
No full textRelative abundance of coccolithophore species in MedSeA-S3 sediment core, spanning from 378 to 1995 years of the Common Era, examined under a polarized microscope at 1000x magnification (size fraction <63 um) at least 500 speciments were counted and identified
Relative abundance of planktonic foraminiferal species in sediment core MedSeA-S3 retrieved from the Alboran Sea during the MedSeA Cruise 2013
No full textRelative abundance of planktonic foraminiferal species in MedSeA-S3 sediment core, spanning from 378 to 1995 years of the Common Era, examined under a stereo microscope (size fraction >125um) at least 300 speciments were counted and identified
Emiliania huxleyi morphological analysis from ODP Site 202-1238
No full textWe present data on the length and mass of Emiliania huxleyi, analyzed by using SYRACO (Systeme de Reconnaissance Automatique de Coccolithes), spanning the last 30 ky at Site ODP 1238 (1°52.310′S, 82°46.934′W; 2203 m; 2203 m) in the Eastern Equatorial Pacific. We also evaluated E. huxleyi calcification index dynamics based on the ratio between the coccolith mass measured with SYRACO and the predicted normalized mass based on Young and Ziveri, 2000
Relative abundance of planktonic foraminiferal species in sediment core MedSeA-S7 retrieved from the Strait of Sicily during the MedSeA Cruise 2013
No full textRelative abundance of planktonic foraminiferal species in MedSeA-S7 sediment core, spanning from 1810 to 2010 years of the Common Era, examined under a stereo microscope (size fraction >125um) at least 300 speciments were counted and identified
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