Sea Surface Temperature Record Research Articles

The amplifying effect of Indonesian Throughflow heat transport on Late Pliocene Southern Hemisphere climate cooling

An unusually short glaciation interrupted the warm Pliocene around 3.3 Ma (Marine Isotope Stage (MIS) M2). Different hypotheses exist to explain why this glaciation event was so pronounced, and why the global climate system returned to warm Pliocene conditions relatively quickly afterwards. One of these proposed mechanisms is a reduced equator-to-pole heat transfer, in response to a tectonically reduced Indonesian Throughflow (ITF). The ITF is a critical part of the global thermohaline ocean circulation, transporting heat from the Indo-Pacific Warm Pool to the Indian Ocean. When ITF connectivity is reduced, the water and heat supply for the Leeuwin Current, flowing poleward along Australia's west coast, is also diminished. To assess the possible relationship between mid-Pliocene glaciations and latitudinal heat transport through the Indonesian Throughflow, we constructed a multi-proxy orbital-scale record for the 3.7–2.8 Ma interval from International Ocean Discovery Program (IODP) Site U1463, off northwest Australia. The comparison of the Site U1463 record with paleoclimate records from nearby Site 763 and West Pacific Warm Pool Site 806 allows for a detailed regional reconstruction of Pliocene paleoceanography and thus for testing the proposed hypothesis.An astronomically-paced decrease in potassium content characterizes the late Pliocene interval of U1463. This record documents the increasing aridity of northwest Australia, periodically alleviated by reinforced summer monsoon precipitation under summer insolation maxima. The δ18O record of the planktonic foraminifer Globigerinoides sacculifer correlates exceptionally well with the sea surface temperature (SST) record from Site 806 in the West Pacific Warm Pool, even during MIS M2. Hence, Site U1463 preserves an uninterrupted ITF signal even during Pliocene glaciations. However, the U1463 δ18OG.sacculifer record exhibits a 0.5‰ offset with the nearby Site 763A record around MIS M2. This implies that Site 763A, about 500 km west of U1463, more closely tracks Indian Ocean SST records across MIS M2. The U1463 data reveal that heat-transport through the Indonesian Throughflow did not shut down completely during MIS M2, but rather its intensity decreased prior to and during MIS M2, causing Site 763A to temporarily reflect an Indian Ocean, rather than an ITF signal. We conclude that ITF variability significantly influenced latitudinal heat transport by means of the Leeuwin Current and hence contributed to the relative intensity of MIS M2. We propose the ITF valve between the Pacific and Indian Ocean as a positive feedback mechanism, in which an initial sea level lowering reduces ITF heat transport, in turn amplifying global cooling by advancing the thermal isolation of Antarctica.

Synchronous tropical and polar temperature evolution in the Eocene.

Palaeoclimate reconstructions of periods with warm climates and high atmospheric CO2 concentrations are crucial for developing better projections of future climate change. Deep-ocean1,2 and high-latitude3 palaeotemperature proxies demonstrate that the Eocene epoch (56 to 34 million years ago) encompasses the warmest interval of the past 66 million years, followed by cooling towards the eventual establishment of ice caps on Antarctica. Eocene polar warmth is well established, so the main obstacle in quantifying the evolution of key climate parameters, such as global average temperature change and its polar amplification, is the lack of continuous high-quality tropical temperature reconstructions. Here we present a continuous Eocene equatorial sea surface temperature record, based on biomarker palaeothermometry applied on Atlantic Ocean sediments. We combine this record with the sparse existing data4-6 to construct a 26-million-year multi-proxy, multi-site stack of Eocene tropical climate evolution. We find that tropical and deep-ocean temperatures changed in parallel, under the influence of both long-term climate trends and short-lived events. This is consistent with the hypothesis that greenhouse gas forcing7,8, rather than changes in ocean circulation9,10, was the main driver of Eocene climate. Moreover, we observe a strong linear relationship between tropical and deep-ocean temperatures, which implies a constant polar amplification factor throughout the generally ice-free Eocene. Quantitative comparison with fully coupled climate model simulations indicates that global average temperatures were about 29, 26, 23 and 19 degrees Celsius in the early, early middle, late middle and late Eocene, respectively, compared to the preindustrial temperature of 14.4 degrees Celsius. Finally, combining proxy- and model-based temperature estimates with available CO2 reconstructions8 yields estimates of an Eocene Earth system sensitivity of 0.9 to 2.3 kelvin per watt per square metre at 68 per cent probability, consistent with the high end of previous estimates11.

A 450-kyr planktonic foraminiferal assemblage record of IODP site U1352 and its implications for the migration of the subtropical front in the south-west Pacific

Abstract The Subtropical Front (STF) is one of the major ocean fronts in the south-west Pacific. The STF migration has a distinct but varying impact on the temperature change throughout the region. To improve our understanding on the history of the STF migration and the relationship between STF migration and global climate change, we have generated a 450-kyr record of sea surface temperature (SST) change at IODP Site U1352 located in the Canterbury Basin off New Zealand. Planktonic foraminiferal assemblages from the site were used to derive SST estimates. Comparisons of the planktonic foraminiferal assemblage and SST record of IODP Site U1352 with those of ODP Site 1119, DSDP Site 594 and core MD06-2986 allow us to reconstruct the spatial change of the STF over the last 450 kyr by locating the positions of its Southland Front (SF) section, which runs nearly parallel to the South Island's shoreline. The percentage of Neogloboquadrina pachyderma in the sum of Nq. pachyderma and Nq. incompta was below 40% at Sites IODP U1352, ODP 1119 and DSDP 594 during Marine Isotope Stage (MIS) 11c, MIS 7a–c and MIS 5e. Moreover, the SSTs of the three sites during these periods were similar and close to that of the present-day. This indicates that the three sites were covered by a Subtropical Water–Subantarctic Water (STW–SAW) mixture during these interglacials. IODP Site U1352 recorded a similar scenario during MIS 7e. In comparison with previous studies, the higher resolution record of IODP Site U1352 showed the influence of an STW–SAW mixture was limited to MIS 11c, MIS 7e, MIS 7a–c and MIS 5e at this site. The SSTs of Sites IODP U1352, ODP 1119 and DSDP 594 were similar during MIS 11a–b and MIS 9a–d. At the same time, the temperature differences among the three sites and core MD06-2986 (west of New Zealand) during MIS 11a–b and MIS 9a–d were larger than during interglacials MIS 11c, MIS 7a–c, and MIS 5e. These indicate that the Subantarctic Water (SAW) influenced Sites IODP U1352, ODP 1119 and DSDP 594 during MIS 11a–b and MIS 9a–d. The ~3–4 °C warmer SSTs at Sites IODP U1352 and ODP 1119 than at DSDP Site 594 suggest that the SF is situated between DSDP Site 594 and Sites IODP U1352, ODP 1119 during MIS 7d and glacial periods of MIS 10, MIS 8, and MIS 6. Hence, unlike previous studies in the region, MIS 7d is identified as a glacial period.

Evaluating biases in sea surface temperature records using coastal weather stations

Sea surface temperatures form a vital part of global mean surface temperature records. Historical observation methods have changed substantially over time from buckets to engine‐room intake sensors, hull sensors and drifting buoys, rendering their use for climatological studies problematic. There are substantial uncertainties in the relative biases of different observations which may impact the global temperature record.Island and coastal weather stations can be compared to coastal sea surface temperature observations to obtain an assessment of changes in bias over time. The process is made more challenging by differences in the rate of warming between air temperatures and sea surface temperatures, and differences across coastal boundaries. A preliminary sea surface temperature reconstruction homogenized using coastal weather station data suggests significant changes to the sea surface temperature record, although there are substantial uncertainties, only some of which can be quantified. A large warm excursion in versions 4 and 5 of the NOAA Extended Reconstructed Sea Surface Temperature during World War 2 is rejected, as is a cool excursion around 1910 present in all existing records. The mid‐century plateau is cooler than in existing reconstructions.

Northern Galápagos Corals Reveal Twentieth Century Warming in the Eastern Tropical Pacific

AbstractModels and observations disagree regarding sea surface temperature (SST) trends in the eastern tropical Pacific. We present a new Sr/Ca‐SST record that spans 1940–2010 from two Wolf Island corals (northern Galápagos). Trend analysis of the Wolf record shows significant warming on multiple timescales, which is also present in several other records and gridded instrumental products. Together, these data sets suggest that most of the eastern tropical Pacific has warmed over the twentieth century. In contrast, recent decades have been characterized by warming during boreal spring and summer (especially north of the equator), and subtropical cooling during boreal fall and winter (especially south of the equator). These SST trends are consistent with the effects of radiative forcing, mitigated by cooling due to wind forcing during boreal winter, as well as intensified upwelling and a strengthened Equatorial Undercurrent.

Stability Assessment of the (A)ATSR Sea Surface Temperature Climate Dataset from the European Space Agency Climate Change Initiative

Sea surface temperature is a key component of the climate record, with multiple independent records giving confidence in observed changes. As part of the European Space Agencies (ESA) Climate Change Initiative (CCI) the satellite archives have been reprocessed with the aim of creating a new dataset that is independent of the in situ observations, and stable with no artificial drift (<0.1 K decade−1 globally) or step changes. We present a method to assess the satellite sea surface temperature (SST) record for step changes using the Penalized Maximal t Test (PMT) applied to aggregate time series. We demonstrated the application of the method using data from version EXP1.8 of the ESA SST CCI dataset averaged on a 7 km grid and in situ observations from moored buoys, drifting buoys and Argo floats. The CCI dataset was shown to be stable after ~1994, with minimal divergence (~0.01 K decade−1) between the CCI data and in situ observations. Two steps were identified due to the failure of a gyroscope on the ERS-2 satellite, and subsequent correction mechanisms applied. These had minimal impact on the stability due to having equal magnitudes but opposite signs. The statistical power and false alarm rate of the method were assessed.

The dynamics of Kelp Forests in the Northeast Pacific Ocean and the relationship with environmental drivers

Abstract The dynamics of foundation species in ecosystems are key to the fate of many species. Kelp forests are foundation species in temperate ocean ecosystems and contribute to carbon storage, macronutrient dynamics, primary production and biodiversity of a myriad of associated species. Downward trends in their abundance globally have been of concern. We analysed 26 years of aerial censuses (1989–2015) of two canopy kelp species in Washington State (USA) waters. We compared these modern censuses with censuses in 1911 and 1912 to determine the persistence of kelp cover over the past century. Using Autoregressive Integrated Moving Average (ARIMA) models, we compared kelp dynamics with likely environmental drivers, including local environmental variables and ocean indices for this region. Kelp remains at historic levels in many areas, although some eastern populations in proximity to greater human populations are the exception to this pattern. Over the last 26 years, kelp abundance showed high spatial autocorrelation in western areas of Straits of Juan de Fuca, with more variable populations in the annual species and eastward towards Puget Sound. Both species covaried positively in their abundance throughout most of the study area, suggesting that environmental factors rather than competition, drove their dynamics. The population dynamics of these kelp species showed that the abundance 1 year previously was an important predictor, and cyclic dynamics were not indicated using ARIMA models. Kelp abundance correlated inversely with the Pacific Decadal Oscillation and the Oceanic Nino Index, and positively with the North Pacific Gyre Oscillation, indicating that large‐scale processes associated with colder seawater temperatures were associated with greater relative abundance of kelp. Synthesis. Kelp beds in the northern California Current Large Marine Ecosystem have mostly remained persistent over the past century and over many kilometres, but some areas may have decreased in abundance. The sensitivity of these populations to indices of ocean climate, our demonstration that a historic 93‐year sea surface temperature record (Race Rocks, Canada) showed a 0.72°C increase and the classification of some areas as high variability‐low abundance, suggest that the viability of these foundational species remain a concern into the future.

Climate induced human demographic and cultural change in northern Europe during the mid-Holocene

The transition from hunter-gatherer-fisher groups to agrarian societies is arguably the most significant change in human prehistory. In the European plain there is evidence for fully developed agrarian societies by 7,500 cal. yr BP, yet a well-established agrarian society does not appear in the north until 6,000 cal. yr BP for unknown reasons. Here we show a sudden increase in summer temperature at 6,000 cal. yr BP in northern Europe using a well-dated, high resolution record of sea surface temperature (SST) from the Baltic Sea. This temperature rise resulted in hypoxic conditions across the entire Baltic sea as revealed by multiple sedimentary records and supported by marine ecosystem modeling. Comparison with summed probability distributions of radiocarbon dates from archaeological sites indicate that this temperature rise coincided with both the introduction of farming, and a dramatic population increase. The evidence supports the hypothesis that the boundary of farming rapidly extended north at 6,000 cal. yr BP because terrestrial conditions in a previously marginal region improved.

Indian Ocean corals reveal crucial role of World War II bias for twentieth century warming estimates

The western Indian Ocean has been warming faster than any other tropical ocean during the 20th century, and is the largest contributor to the global mean sea surface temperature (SST) rise. However, the temporal pattern of Indian Ocean warming is poorly constrained and depends on the historical SST product. As all SST products are derived from the International Comprehensive Ocean-Atmosphere dataset (ICOADS), it is challenging to evaluate which product is superior. Here, we present a new, independent SST reconstruction from a set of Porites coral geochemical records from the western Indian Ocean. Our coral reconstruction shows that the World War II bias in the historical sea surface temperature record is the main reason for the differences between the SST products, and affects western Indian Ocean and global mean temperature trends. The 20th century Indian Ocean warming pattern portrayed by the corals is consistent with the SST product from the Hadley Centre (HadSST3), and suggests that the latter should be used in climate studies that include Indian Ocean SSTs. Our data shows that multi-core coral temperature reconstructions help to evaluate the SST products. Proxy records can provide estimates of 20th century SST that are truly independent from the ICOADS data base.

Northern South China Sea SST changes over the last two millennia and possible linkage with solar irradiance

High-resolution surface temperature records over the last two millennia are crucial to understanding the forcing and response mechanism of Earth's climate. Here we report a bidecadal-resolution sea surface temperature (SST) record based on long-chain alkenones in a gravity sediment core retrieved from the northern South China Sea. SST values varied between 26.7 and 27.5 °C, with a total variability ∼1 °C over the last 2000 years. The general SST variation pattern matches well with total solar irradiance (TSI) changes. Relatively warm period between 800 and 1400 AD and cool period 1400-1850 AD could be identified, in agreement with the commonly defined periods of Medieval Warm Period and Little Ice Age. Within chronological uncertainty, notable short cooling events at 640-670 AD, 1030-1080 AD, 1260-1280 AD and 1420-1450 AD, coincide with large volcanic eruption events. The general coincidence of SST changes with TSI and volcanic eruption events suggests strong impact of external forcing on sea surface conditions in the studied area. In addition to the direct TSI changes, volcanic eruptions might have induced oceanic and atmospheric circulation adjustments which might be responsible for the short cooling events as revealed in the alkenone-SST record.

A 1-Ma record of sea surface temperature and extreme cooling events in the North Atlantic: A perspective from the Iberian Margin

The Iberian Margin is a sensitive area to track high and low latitude processes, and is a key location to understand major past climatic and oceanographic changes. Here we present new biomarker data from IODP Site U1385 (“Shackleton site”) (1017–336 ka) that, when combined with existing data from Cores MD01-2443/4 (last 335 ka), allows us to assess the evolution of sea surface temperature (SST) and meltwater influx over the last 1 Ma at the Iberian Margin. Interglacial periods throughout the last 1 Ma show SST close to 20 °C, even during the so-called “luke-warm” interglacials that are marked by relatively low atmospheric CO2 concentrations. During glacial periods, extremely cold stadial events are recognized at the Iberian Margin, and are very likely related to meltwater discharges from the European and British-Irish ice sheets into the NE Atlantic, which were transported southwards by the Portugal Current. We subdivided the record into four intervals on the basis of the timing and the magnitude of these extremely cold stadials: 1) from 1017 to ∼900 ka, only minor sporadic freshwater input occurred during deglaciations; 2) from 900 to 675 ka extreme cold events occur as terminal stadial events at the beginning of the deglaciations, which results in abrupt deglacial SST shifts; 3) from 675 to 450 ka only a few, very short-lived events are recorded and seldom is there freshwater input at the Iberian Margin; 4) during the last 450 ka the extreme cold events occurred under full glacial conditions, with particularly severe events during MIS 6 and 8. We propose these mid –glacial events are associated with a strong discharges of European ice sheet (EIS). The fact that these extreme cold events do not coincide with deglaciations questions the role of European ice sheet discharges in triggering deglaciations.

Reconstruction of oceanic circulation patterns in the tropical Pacific across the early/middle Miocene boundary as inferred from radiolarian assemblages

Although there have been attempts to infer Neogene oceanic circulation patterns in the tropical Pacific on the basis of multiple marine proxies, oceanic circulation patterns across the early/middle Miocene boundary are still poorly understood despite paleoclimate having significantly changed during this interval. In this study, we reconstruct the changes in tropical oceanic circulation patterns in the Pacific across the early/middle Miocene boundary based on radiolarian assemblages obtained at Integrated Ocean Drilling Program Site U1335 in the eastern tropical Pacific.The radiolarian upwelling taxa increased during four intervals (18.4–18.1Ma, 16.9–15.7Ma, 15.2–14.6Ma, 14.2–13.4Ma). Radiolarian temperature index (RTI) was calculated using the relative abundances of the warm water (cluster B1) and cool water taxa (cluster B2) in order to evaluate relative temperature fluctuations of the surface water. The sea surface temperature index was relatively high from 16.8 to 16.0Ma and gradually decreased from 16.0 to 14.6Ma. Subsequently, the temperature index decreased stepwise at 13.9 and 13.4Ma and became relatively low from 13.4 to 12.7Ma. Comparison of the RTI record in the eastern tropical Pacific to the climatic index based on the benthic foraminiferal δ18O record shows that variability in the two records follows a roughly similar trend from the early to the middle Miocene. However, the sea surface temperature record does not indicate a sharp increase in warmth in the eastern tropical Pacific during the mid-Miocene climatic Optimum-1 (MMCO-1), as suggested by the benthic isotopic record. This is likely because of increased upwelling of cool, nutrient-rich water at this time.Beginning in the latest early Miocene (~17Ma) radiolarian assemblages were dominated by different taxa in the eastern and western tropical Pacific. This pattern is interpreted as indicating a shallower thermocline in the east and a deeper thermocline in the west, based on the relative abundance of the upwelling taxa. There is an overall increasing trend in this difference since the latest early Miocene. We tie these events to the effective closure of the Indo-Pacific seaway and the development of a substantial western Pacific warm pool along with the development of a strong Equatorial Undercurrent.

Nonlinear climatic sensitivity to greenhouse gases over past 4 glacial/interglacial cycles

The paleoclimatic sensitivity to atmospheric greenhouse gases (GHGs) has recently been suggested to be nonlinear, however a GHG threshold value associated with deglaciation remains uncertain. Here, we combine a new sea surface temperature record spanning the last 360,000 years from the southern Western Pacific Warm Pool with records from five previous studies in the equatorial Pacific to document the nonlinear relationship between climatic sensitivity and GHG levels over the past four glacial/interglacial cycles. The sensitivity of the responses to GHG concentrations rises dramatically by a factor of 2–4 at atmospheric CO2 levels of >220 ppm. Our results suggest that the equatorial Pacific acts as a nonlinear amplifier that allows global climate to transition from deglacial to full interglacial conditions once atmospheric CO2 levels reach threshold levels.

Recent enhancement of central Pacific El Ni\xf1o variability relative to last eight centuries

The far-reaching impacts of central Pacific El Niño events on global climate differ appreciably from those associated with eastern Pacific El Niño events. Central Pacific El Niño events may become more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NIÑO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Niño4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Niño-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.

Monsoonal upwelling in the western Arabian Sea since the middle Miocene

Research Article| July 01, 2017 Monsoonal upwelling in the western Arabian Sea since the middle Miocene Guangsheng Zhuang; Guangsheng Zhuang 1Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA Search for other works by this author on: GSW Google Scholar Mark Pagani; Mark Pagani 2Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA Search for other works by this author on: GSW Google Scholar Yi Ge Zhang Yi Ge Zhang 3Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA Search for other works by this author on: GSW Google Scholar Author and Article Information Guangsheng Zhuang 1Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana 70803, USA Mark Pagani 2Department of Geology and Geophysics, Yale University, New Haven, Connecticut 06520, USA Yi Ge Zhang 3Department of Oceanography, Texas A&M University, College Station, Texas 77843, USA Publisher: Geological Society of America Received: 01 Feb 2017 Revision Received: 21 Mar 2017 Accepted: 21 Mar 2017 First Online: 28 Jun 2017 Online Issn: 1943-2682 Print Issn: 0091-7613 © 2017 Geological Society of America Geology (2017) 45 (7): 655–658. https://doi.org/10.1130/G39013.1 Article history Received: 01 Feb 2017 Revision Received: 21 Mar 2017 Accepted: 21 Mar 2017 First Online: 28 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Guangsheng Zhuang, Mark Pagani, Yi Ge Zhang; Monsoonal upwelling in the western Arabian Sea since the middle Miocene. Geology 2017;; 45 (7): 655–658. doi: https://doi.org/10.1130/G39013.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Asian monsoon has long been argued to be a product of the Himalaya–Tibetan Plateau, and simulation experiments have confirmed the key role of the Himalaya–Tibetan Plateau in transforming regional atmospheric and oceanic circulations. However, temporal constraints on the strengthening of the Asian monsoon inferred from foraminifer isotopic and faunal data and terrestrial climatic and ecological records are inconsistent with each other, which has obscured the tectonic-climatic linkage. In particular, discriminating the post-middle Miocene global cooling from the monsoon upwelling cooling is critical, but poorly understood due to the lack of adequate constraints for monsoonal upwelling. Here we present new middle to late Miocene biomarker-based reconstructions of sea-surface temperature (SST) for the western Arabian Sea. Our new SSTs capture a long-term ocean cooling since ca. 14.8 Ma and a major drop in SST in the period 11–10 Ma after which the SSTs reached similar values as the Holocene. The new SST record is consistent with planktonic foraminifer, siliceous biota, and geochemical tracer studies, suggestive of ocean cooling and high productivity associated with monsoonal upwelling. The 11–10 Ma ocean cooling is not clearly expressed in other tropical oceans, indicating that the ocean cooling in the western Arabian Sea is not a simple reflection of global cooling. We interpret the 11–10 Ma ocean cooling as representing the establishment of monsoonal upwelling in the western Arabian Sea, triggered by strong cyclonic activities as a result of the Neogene outward expansion of the Himalaya–Tibetan Plateau. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Latest Cretaceous climatic and environmental change in the South Atlantic region

Latest Maastrichtian climate change caused by Deccan volcanism has been invoked as a cause of mass extinction at the Cretaceous-Paleogene (K-Pg) boundary (~66.0 Ma). Yet late Maastrichtian climate and ecological changes are poorly documented, in particular on the Southern Hemisphere. Here we present upper Maastrichtian-lower Danian climate and biotic records from the Bajada del Jaguel (BJ) shelf site (Neuquen Basin, Argentina), employing the TEX86 paleothermometer, marine palynology (dinoflagellate cysts), and micropaleontology (foraminifera). These records are correlated to the astronomically tuned Ocean Drilling Program Site 1262 (Walvis Ridge). Collectively, we use these records to assess climatic and ecological effects of Deccan volcanism in the Southern Atlantic region. Both the TEX86-based sea surface temperature (SST) record at BJ and the bulk carbonate δ18O-based SST record of Site 1262 show a latest Maastrichtian warming of ~2.5–4°C, at 450 to 150 kyr before the K-Pg boundary, coinciding with the a large Deccan outpouring phase. Benthic foraminiferal and dinocyst assemblage changes indicate that this warming resulted in enhanced runoff and stratification of the water column, likely resulting from more humid climate conditions in the Neuquen Basin. These climate conditions could have been caused by an expanding and strengthening thermal low over the South American continent. Biotic changes in response to late Maastrichtian environmental changes are rather limited, when compared to the major turnovers observed at many K-Pg boundary sites worldwide. This suggests that environmental perturbations during the latest Maastrichtian warming event were less severe than those following the K-Pg boundary impact.

Sea-surface temperatures for the last 7200 years from the eastern Sunda Shelf, South China Sea: Climatic inferences from planktonic foraminiferal Mg/Ca ratios

To test whether low latitude shallow shelf deposits can provide high resolution paleoclimatic records, we utilized two cores from the Holocene sedimentary fill of incised valleys on the Sunda Shelf off Sarawak, Malaysia. We developed a new sea-surface temperature (SST) record based on planktonic foraminiferal Mg/Ca for the last 7200 years. This record reveals several significant shifts between warmer and colder conditions. Temperatures averaged 27.5 °C ca. 7200 cal. years BP, then climbed to 28.2 °C from 6500 to 5500 cal. years BP. At 5500-4500 cal. years BP we identified the coldest period (26.8 °C) of the analyzed period. For the last 4500 years SST again averaged 27.5 °C but the profile is rather variable. The last ca. 1000 years recorded the warmest SST averaging 28.5 °C. We record, for the first time in this region, a cool interval, ca. 1000 years in duration, centered on 5000 cal years BP concomitant with a wet period recorded in Borneo. The record also reflects a warm interval from ca. 1000 to 500 cal years BP that may represent the Medieval Climate Anomaly.Variations in the East Asian Monsoon (EAM) and solar activity are considered as potential drivers of SST trends. However, hydrology changes related to the El Niño-Southern Oscillation (ENSO) variability, shifts of the Western Pacific Warm Pool and migration of the Intertropical Convergence Zone are more likely to have impacted our SST temporal trend. Our findings indicate that climatic patterns in the region might be in phase with ENSO and out of phase with the EAM.

Geochemical composition of Tanzanian shelf sediments indicates Holocene climatic and sea-level changes

AbstractWe present a high-resolution geochemical and grain-size record from a Holocene sediment core off the Pangani River mouth, Tanzania. Elemental ratios between biogenic elements and Al (i.e., Ca/Al, Mg/Al, and Sr/Al) are mainly influenced by terrigenous dilution on carbonate concentration and/or limitation of carbonate production as a result of variations in the supply of fine-grained terrigenous sediments of the Pangani River. Such elemental ratios increased significantly at the end of the mid-Holocene between 5 and 3.5 ka, demonstrating a gradual transition from the humid early and mid-Holocene to the arid late Holocene in East Africa. Among the elemental ratios between terrigenous elements and Al, Si/Al and K/Al ratios correlate to grain-size variation, indicating a change in sedimentation regime. Fe/Al and Ti/Al ratios show that the sediment source area has shifted from the terrestrial volcanic region of Tanzania (Fe, Ti rich) to the coastal and inner-shelf regions (Fe, Ti poor) around 7.5 ka, in response to arid climate and high sea level. Our geochemical results correspond with a sea-surface temperature record derived from the same sediment core, indicating that the end of the East African Humid Period could have been gradual and related to the cooling water in the western Indian Ocean.

Diploastrea heliopora Sr/Ca and δ18O records from northeast Luzon, Philippines: An assessment of interspecies coral proxy calibrations and climate controls of sea surface temperature and salinity

AbstractThe Indo‐Pacific coral Diploastrea heliopora reveals regional multidecadal‐ to centennial‐ scale climate variability using coral carbonate δ18O (δ18Oc) as a combined proxy for sea surface temperature (SST) and sea surface salinity (SSS). However, to assess the coral's full potential in resolving climatic events, an independent SST proxy would be more advantageous. We examined both Sr/Ca and δ18O of Diploastrea against an adjacent Porites lobata core collected from northeast Luzon, Philippines. Winter Sr/Ca data from Diploastrea show a significant correlation to SST (r = −0.41, p < 0.05, (root‐mean‐square of the residual) RMSR = 0.81°C) and provide a proxy with similar sensitivity as Porites (r = −0.57, p < 0.05, RMSR = 0.62°C). An interspecies SST record is shown to be robust and used for a reconstruction of the Pacific Decadal Oscillation during boreal winter (r = −0.70, p = 0.02). While we were unable to generate a robust Diploastrea δ18O‐SSS calibration at interannual timescale, the freshening trend toward the present, commonly observed in the region, is qualitatively captured in Diploastrea δ18O. Comparison with Porites δ18O and instrumental SSS records shows that the magnitude of freshening is consistent between coral species. Wet and dry season Porites δ18O provide support for the relative influence of El Niño–Southern Oscillation events and local precipitation to SSS variability at our site. The multiproxy, multispecies approach of this study further strengthens the evidence for Diploastrea as an alternate climate archive in the Indo‐Pacific region and seals its potential in helping resolve less understood global‐scale climate phenomena.

A Holocene record of ocean productivity and upwelling from the northern California continental slope

The Holocene upwelling history of the northern California continental slope is examined using the high-resolution record of TN062-O550 (40.9°N, 124.6°W, 550 m water depth). This 7-m-long marine sediment core spans the last ∼7500 years, and we use it to test the hypothesis that marine productivity in the California Current System (CCS) driven by coastal upwelling has co-varied with Holocene millennial-scale warm intervals. A combination of biogenic sediment concentrations (opal, total organic C, and total N), stable isotopes (organic matter δ13C and bulk sedimentary δ15N), and key microfossil indicators of upwelling were used to test this hypothesis. The record of biogenic accumulation in TN062-O550 shows considerable Holocene variability despite being located within 50 km of the mouth of the Eel River, which is one of the largest sources of terrigenous sediment to the Northeast Pacific Ocean margin. A key time interval beginning at ∼2900 calibrated years before present (cal yr BP) indicates the onset of modern upwelling in the CCS, and this period also corresponds to the most intense period of upwelling in the last 7500 years. When these results are placed into a regional CCS context during the Holocene, it was found that the timing of upwelling intensification at TN062-O550 corresponds closely to that seen at nearby ODP Site 1019, as well as in the Santa Barbara Basin of southern California. Other CCS records with less refined age control show similar results, which suggest late Holocene upwelling intensification may be synchronous throughout the CCS. Based on the strong correspondence between the alkenone sea surface temperature record at ODP Site 1019 and the onset of late Holocene upwelling in northern California, we suggest that CCS warming may be conducive to upwelling intensification, though future changes are unclear as the mechanisms forcing SST variability may differ.