Long-chain Alkenones Research Articles

Long-Chain Alkenones in the South Yellow Sea Sediments and Their Indicative Significance for Haptophytes Species

Long-Chain Alkenones in the South Yellow Sea Sediments and Their Indicative Significance for Haptophytes Species

Large variability and 2H-depletion of Middle Miocene to Pleistocene alkenone hydrogen isotopes in the Equatorial Pacific reflect subsurface, low light haptophyte growth

Hydrogen isotope ratios of haptophyte derived long-chain alkenones (δ2HC37:2) have shown to be a useful tool for reconstructing past isotopic compositions of surface seawater (δ2HSSW). The δ2HSSW is related to global ice volume, sea surface salinity and the local hydrological cycle. Here, we present a hydrogen isotope record of alkenones spanning the last 14.5 Ma from IODP site U1338 in the east equatorial Pacific. The alkenone-based reconstructed δ2HSSW is substantially more negative and variable than reconstructed δ2HSSW based on published oxygen isotopes of coccolith carbonates. This suggests that factors other than the isotopic composition of seawater affect the hydrogen isotopic composition of alkenones. The relatively negative and highly variable δ2HC37:2 values are in line with published modern observations on alkenones from suspended particulate matter in the equatorial and north Pacific, with the highest values at relatively high light conditions at the surface and the lowest values at higher water depth and relatively low light conditions. This suggests that the relatively negative and highly variable δ2HC37:2 values in these Middle Miocene to Pleistocene sediments are likely derived from haptophytes growing below the sea surface under variable low light conditions. In regions where the contribution of alkenones from subsurface production, due to high subsurface nutrients, at low light intensities to the sediment is relatively high the δ2HC37:2 has to be interpreted with care as a proxy for δ2HSSW.

Temperature-dependent carbon isotope fractionation in coccolithophores

Introduction: The stable carbon isotope ratio of long-chain alkenones produced by marine haptophyte phytoplankton has often been used to estimate past variations in atmospheric CO2 throughout the Cenozoic. However, previous experimental studies and surveys of alkenones from surface sediment and suspended particulate matter document additional environmental and physiological influences on carbon isotopic fractionation in alkenones.Methods: To clarify the non-CO2 effects on the alkenone carbon isotope fractionations, an important alkenone producer, Gephyrocapsa oceanica, was cultured in laboratory. To separate effects of different environment parameters, G. oceanica was grown in continuous cultures under a matrix of environmental conditions in order to explore the influence of temperature independently of CO2(aq). Through careful manipulation of the media carbon system, we can control the variation of the media CO2(aq) independently of temperature solubility. Carbon isotope fractionations from alkenones, coccolith, and particulate organic carbon were measured from this steady state system.Results and Discussion: We find εp in alkenones and particulate organic carbon inversely correlates with temperature, and temperature affects εp more strongly than CO2(aq). The magnitude of the temperature effect can be explained by higher growth rates at warmer temperatures with a similar growth rate dependence as observed in previous cultures in which growth rate was regulated by other factors. Where the past temperature influence on growth rate could be constrained using the UK’37 alkenone index in the same samples, our finding offers an approach to deconvolve an important physiological factor affecting ancient alkenones εp, and may therefore improve past pCO2 estimates.

Long-chain alkenones in sediments of Lake Utichye 3 (southern Siberia,Khakassia) as a paleo-indicator of climate change

Long-chain alkenones in sediments of Lake Utichye 3 (southern Siberia,Khakassia) as a paleo-indicator of climate change

Highly efficient purification of long-chain alkenones using silver dimercaptotriazine flash chromatography

Long-chain alkenones (LCAs) are important tools for paleotemperature reconstructions in lacustrine and marine environments. However, some neutral lipid compounds that co-elute with LCAs often occur in natural sediment samples, which seriously interferes with the identification and quantification of the LCAs. In this study, we report a new flash column chromatography based on silver(I)-dimercaptotriazine (Ag-DMT) functionalized silica material (≡Si-DMT-Ag) for purifying and isolating the individual LCAs from complex lake and marine sediment samples. Compared to silver(I)-mercaptopropyl (Ag-MP) functionalized (≡Si-(CH2)3-S-Ag) and silver nitrate (SiO2 + AgNO3) impregnated silica materials used by previous studies, the Ag-DMT stationary phase displays the best efficiency in removing co-eluting compounds (including wax ester, hopanoid, hopanoic acid, sterane, alkanoic acid, and some unknown compounds) from the LCAs in our study lake and marine sediment samples. The Ag-DMT material also shows its high retention capacity for the LCAs, probably due to a strong interaction of more positively charged silver sites on Ag-DMT with double bonds. Employing the Ag-DMT chromatography, we develop an optimal solvent elution scheme to efficiently isolate the individual LCAs with the same chain length but different numbers of unsaturation for their isotopic analysis in the future. Our study provides a highly effective method for eliminating co-eluting compounds and isolating individual LCAs for paleoclimate studies.

Long-Chain Alkenones in Sediments of Lake Utichye-3 (Southern Siberia, Khakassia) as a Paleo-Indicator of Climate Change

Long-Chain Alkenones in Sediments of Lake Utichye-3 (Southern Siberia, Khakassia) as a Paleo-Indicator of Climate Change

Isolation and characterization of an alkenone composition mutant in the haptophyte Tisochrysis lutea

While long-chain alkenone (defined as alkenone) is known to have a potential for industrial application, its biosynthetic pathway is still largely unknown. In the present study, we obtained a novel mutant named C8–14 strain altering alkenone composition with heavy-ion beam irradiation to the haptophyte Tisochrysis lutea. This mutant showed higher levels of tri-unsaturated alkenones and significantly lower amounts of alkenones and alkenoates than the wild-type cells. In addition, the total amounts of fatty acids in the neural lipid fraction of the C8–14 strain were higher than those in the wild-type cells. The primary sequence of the genes related to alkenone desaturases in the C8–14 strain, including the paralogous genes found in this study, were identical to those in the wild-type cells. However, the expression level of the putative alkenone desaturase gene was altered. The expression of the TOD-2 gene was slightly higher in the C8–14 cells than in the wild-type cells. This is the first report, to the best of our knowledge, to create the mutant with the altered unsaturation of alkenones.

Abrupt cooling of cold seasons at the middle-late Holocene transition revealed by alkenone records from North China

In saline lakes, the paleoenvironmental interpretation of long-chain alkenones (LCAs) is difficult due to the inputs of Isochrysidales Group 2i, which are ice-related bloomers. Here, we perform detailed analysis of LCAs and long-chain alkenoates in sediment cores from Lake Daihai in north China. During the late Holocene, alkenone-inferred temperatures and the Group 2i species abundance indicate a long-term warming trend in cold seasons (winter and early spring), possibly driven by regional insolation and by atmospheric CO2 concentrations. Notably, our records indicate cold climate conditions during the period of 4.3–3.0 cal ka BP, possibly linked to the abrupt expansion of Arctic winter sea ice in a given of low insolation and atmospheric CO2 concentration conditions. The abrupt cooling may have led to the collapse of the East Aian Summer Monsoon (EASM) and the deterioration of the ecosystems in northern China during the middle to late Holocene transition, and thus likely accounted for the nearly synchronous Chinese Neolithic cultural collapses.

Lipid-based paleoecological and biogeochemical reconstruction of Store Saltsø, an extreme lacustrine system in SW Greenland

Polar lakes harbour a unique biogeochemistry that reflects the implications of climatic fluctuations against a susceptible yet extreme environment. In addition to polar, Store Saltsø (Kangerlussuaq, southwestern Greenland) is an endorheic lake with alkaline and oligotrophic waters that host a distinctive ecology adapted to live in such particular physico-chemical and environmental conditions. By exploring the sedimentary record of Store Saltsø at a molecular and compound-specific isotopic level, we were able to understand its ecology and biogeochemical evolution upon climate change. We employed lipid biomarkers to identify biological sources and metabolic traits in different environmental samples (shore terrace, sediment core, and white precipitates at the shore), and their succession over time to reconstruct the lake paleobiology. Different molecular ratios and geochemical proxies provided further insights toward the evolution of environmental conditions in the frame of the deglaciation history of Kangerlussuaq. The relative abundance of terrestrial (i.e., plant derived) biomarkers (odd long-chain n-alkanes, even long-chain n-alkanols, and phytosterols) in the upper half of the shore terrace versus the relatively more present aquatic biomarkers (botryococcenes and long-chain alkenones) in its lower half revealed higher lake water levels in the past. Moreover, the virtual absence of organics in the deepest section of the sediment core (32–29 cm depth) suggested that the lake did not yet exist at the northwestern shore of Store Saltsø ∼5100 years ago. According to the relative abundance of lipid biomarkers detected in the adjacent section above (29–25 cm depth), we hypothesize that the northwestern shore of Store Saltsø formed ∼4900 years ago. By combining the molecular and compound-specific isotopic analysis of lipids in a ∼360 cm sedimentary sequence, we recreated the paleobiology and evolution of an extreme lacustrine environment suitable for the study of the limits of life and the effects of climate warming.

Polyunsaturated long-chain alkenones in the lake sediments of North-Minusinsk valley (southern Siberia) as a paleo-indicator of climate change

The research of biochemical thermo- and salt-sensitive markers - long-chain alkenones in sediments of lakes of the North Minusinsk valley is an important contribution to the understanding of climatic changes in this region. We found that the total concentration of alkenones in the top layers of bottom sediments of saline lakes increases significantly at a salinity of about 20 g l-1. Also, it was found that the average chain length of alkenones in the surface sediments rises with increasing salinity and thus can be used as an indicator of salinity, and the ratio of alkenones C37/C38 varies widely, suggesting that this index can be used as a paleo-indicator of salinity. The high correlation between ,  and  indices with salinity indicates their potential for paleosalinity reconstruction. The obtained functional dependences were additionally verified in the core of bottom sediments of Lake Utichie-3 and confirmed the possibility of using alkenones as a paleo-indicator of climatically determined salinity changes in endorheic lakes. The taxonomic composition of haptophyte algae and alkenone composition in the studied lakes were comparable to lakes in prairie regions of North America.

Glacial–interglacial seawater isotope change near the Chilean Margin as reflected by δ2H values of C37 alkenones

Abstract. Stable hydrogen isotopic compositions of long-chain alkenones with 37 carbon atoms (δ2HC37) have been shown to reflect seawater salinity in culture and environmental studies, and this potential sea surface salinity proxy has been applied to several downcore records from different regions. However, previous studies were based solely on a single sediment core and often suggested unlikely large changes in salinity based on existing proxy calibrations. Here we present a new δ2HC37 record, in combination with oxygen isotopes of benthic foraminifera from the same samples, from a sediment core from the Chilean Margin (ODP Site 1235). The observed negative shift in δ2HC37 of 20 ‰ during the last deglaciation was identical to that of a previously published δ2HC37 record from the nearby, but deeper, ODP Site 1234, suggesting a regionally consistent shift in δ2HC37. This change translates into a negative hydrogen isotope shift in the surface seawater of ca. 14 ‰, similar to glacial–interglacial reconstructions based on other δ2HC37 records. The reconstructed bottom seawater oxygen isotope change based on benthic foraminifera during the last deglaciation is approximately −0.8 ‰, in line with previous studies. When translated into hydrogen isotopes of bottom seawater using the modern open-ocean water line, this would suggest a negative change of ca. 5 ‰, smaller than the reconstructed surface seawater shift based on alkenones. The larger change in surface water isotopes suggests that it experienced more freshening during the Holocene than bottom waters, either due to increased freshwater input, reduced evaporation, or a combination of the two.

Long-chain alkenones in the lake sediments of North-Minusinsk Valley (southern Siberia): implications for paleoclimate reconstructions

Long-chain alkenones (LCAs) are polyunsaturated methyl or ethyl ketones exclusively produced by Groups 1–3 Isochrysidales, an order of haptophyte algae. LCAs have great potential as temperature and salinity proxies for paleo-reconstructions. Alkenone producers occur extensively in lacustrine and in open marine systems. However, factors influencing LCAs occurrence, abundance, compositional pattern, and unsaturation indices are insufficiently understood in lakes of southern Siberia. Here we investigated alkenone distributions in freshwater to saline lakes of a semi-arid region of southern Siberia (n = 22). We find that total alkenone concentrations increase dramatically above a salinity of about 20 g L−1. Analysis of 18S rRNA and the alkenone composition suggest that all alkenone-containing lakes are inhabited by Group 2 haptophytes except one low-saline lake, where Group 1 representatives prevail. The C37/C38 ratio is negatively correlated with salinity, and, hence, this parameter can be used as a salinity indicator. At the same time, %C37:4 is not correlated with salinity, whereas the average chain length of alkenones increases with salinity. The taxonomic composition of haptophytes and the alkenone composition were comparable to those in the lakes in the Canadian Prairies, potentially because of the similarities in climatic factors and ionic composition of lake water in the two regions. This study shows for the first time that unsaturation indexes U40K and U40K′ are positively correlated with salinity and, thus, can be used as a salinity proxy for regional climate reconstruction.

Deglacial increase of seasonal temperature variability in the tropical ocean

The relatively stable Holocene climate was preceded by a pronounced event of abrupt warming in the Northern Hemisphere, the termination of the Younger Dryas (YD) cold period1,2. Although this transition has been intensively studied, its imprint on low-latitude ocean temperature is still controversial and its effects on sub-annual to decadal climate variability remain poorly understood1,3,4. Sea surface temperature (SST) variability at these timescales in the tropical Atlantic is expected to intensify under current and future global warming and has considerable consequences for environmental conditions in Africa and South America, and for tropical Pacific climate5–8. Here we present a 100-µm-resolution record obtained by mass spectrometry imaging (MSI) of long-chain alkenones in sediments from the Cariaco Basin9–11 and find that annually averaged SST remained stable during the transition into the Holocene. However, seasonality increased more than twofold and approached modern values of 1.6 °C, probably driven by the position and/or annual range of the Intertropical Convergence Zone (ITCZ). We further observe that interannual variability intensified during the early Holocene. Our results demonstrate that sub-decadal-scale SST variability in the tropical Atlantic is sensitive to abrupt changes in climate background, such as those witnessed during the most recent glacial to interglacial transition.

Last Interglacial decadal sea surface temperature variability in the eastern Mediterranean

The Last Interglacial (~129,000–116,000 years ago) is the most recent geologic period with a warmer-than-present climate. Proxy-based temperature reconstructions from this interval can help contextualize natural climate variability in our currently warming world, especially if they can define changes on decadal timescales. Here, we established a ~4.800-year-long record of sea surface temperature (SST) variability from the eastern Mediterranean Sea at 1–4-year resolution by applying mass spectrometry imaging of long-chain alkenones to a finely laminated organic-matter-rich sapropel deposited during the Last Interglacial. We observe the highest amplitude of decadal variability in the early stage of sapropel deposition, plausibly due to reduced vertical mixing of the highly stratified water column. With the subsequent reorganization of oceanographic conditions in the later stage of sapropel deposition, when SST forcing resembled the modern situation, we observe that the maximum amplitude of reconstructed decadal variability did not exceed the range of the recent period of warming climate. The more gradual, centennial SST trends reveal that the maximal centennial scale SST increase in our Last Interglacial record is below the projected temperature warming in the twenty-first century.

Group 1 phylogeny and alkenone distributions in a freshwater volcanic lake of northeastern China: Implications for paleotemperature reconstructions

Long-chain alkenones (LCAs) produced by Group 1 Isochrysidales from freshwater lakes feature a highly specific profile with almost the same abundances of two C37 tri-unsaturated alkenone isomers. Their unsaturation ratios have been proposed to have great potential for cold-season paleotemperature reconstructions. However, recent study based on the next-generation sequencing has found that there is high level of genetic diversity in Group 1 Isochrysidales, with two main subclades Groups 1a and 1b. It is still unclear whether variable mixtures of different Group 1 subclades can significantly affect the LCA-based paleotemperature proxies in freshwater lake sediment records. Here we investigated LCA distributions and haptophyte-specific 18S rRNA sequences from a sediment core in Tuofengling Tianchi (a freshwater volcanic lake) of northeastern China using a combination of lipid biomarker and next-generation sequencing analyses. We recover 386 amplicon sequence variants (ASVs) from the studied sediment samples, 11 of which are affiliated with the LCA-producing Isochrysidales. Our phylogenetic analysis identifies that all LCA-producing Isochrysidales belong to Group 1 phylotype (Groups 1a and 1b subclades included), with Group 1a being the dominant subclade in most samples. The phylotype is strongly supported by the LCA evidence of two C37 tri-unsaturated alkenone isomers, with RIK37 (ratio of isomeric ketones of C37 chain length) of ∼ 0.57–0.60. Groups 1a and 1b in our sediment core display significant downcore variations in the relative abundances, with Group 1a ranging from 32% to 100%. However, such highly variable mixtures are not a dominant factor in affecting the values of LCA-based on temperature proxies (U37K, U38KEt, and R3b) in our sediment core. Our study provides the sedimentary evidence that Group 1 LCAs elude species-mixing effects and highlight the potential importance of Group 1 LCAs from freshwater lakes in quantitatively reconstructing past temperature changes.

Long-chain alkenones in the Shimosa Group reveal palaeotemperatures of the Pleistocene interglacial Palaeo-Tokyo Bays

The Shimosa Group, a Middle- to Late-Pleistocene sedimentary succession, has been the focus of stratigraphic attention because it lies beneath the Tokyo metropolitan area of central Japan. It is also of palaeoclimatic significance because it contains important interglacial marine strata of the past 450,000 years. Because the marine strata of the Shimosa Group were formed in the shallow inner bay known as the Palaeo-Tokyo Bay, rare occurrences of planktonic foraminifera make it difficult to quantitatively reconstruct the palaeo-sea surface temperatures (SSTs). Here, we extracted long-chain alkenones (LCAs) from the core GS-UR-1 penetrating the Shimosa Group to Marine Isotope Stage (MIS) 11. We found that the alkenone unsaturation ratio appears to reflect the SST of the Palaeo-Tokyo Bay formed during the peaks of MISs 5e, 7e, 9, and 11, which was consistent with the inflowing water mass changes inferred from the benthic foraminiferal assemblages. The palaeo-SSTs during each interglacial period were 2–3 °C higher than the pre-industrial levels of Tokyo Bay and seemed to reach a level similar to that of the Holocene thermal maximum. The findings of this study demonstrate that the LCA-based proxy, which has not before been utilised in studies on the Shimosa Group, has strong potential to provide palaeoceanic and stratigraphic information.

Long-chain alkenones in the lake sediments of North-Minusinsk Basin (South Siberia): implications for paleoclimate reconstructions

Abstract. The core-top calibration study of 22 lakes indicates that in salt lakes the total alkenones increase sharply at a salinity of about 20 g/L, while alkenones are absent in the sediments of freshwater lakes. For the first time, this study shows that the Uk40 and Uk40 unsaturation indices are positively correlated with salinity and thus can be used to reconstruct salinity. The C37/C38 ratio is negatively correlated with salinity, and therefore this parameter can be used as an indicator of salinity. Also, the %C37:4 indicator is not correlated with salinity. It was found that the average chain length of alkenones increases with salinity, but the correlation was weak. Analysis of the alkenone composition and 18S rRNA suggests that all lakes are inhabited by Group II haptophytes, except for one freshwater lake, where the Group I of LCA-producing haptophytes was found. The taxonomic composition of haptophyte algae and the alkenone composition in the lakes were comparable to those in the lakes of the Canadian Prairies, apparently due to the similarity of climatic factors and the ionic composition of lake water in the two regions.

Phylogeny, alkenone profiles and ecology of Isochrysidales subclades in saline lakes: Implications for paleosalinity and paleotemperature reconstructions

Long-chain alkenones (LCAs) produced by phylogenetically classified Groups 1 and 3 Isochrysidales are increasingly used for paleotemperature and/or paleosalinity reconstructions in oligohaline lakes and marine environments. However, there are considerable difficulties in the paleoenvironmental interpretation of LCAs from Group 2 Isochrysidales thriving in saline lakes. The biggest challenge lies in our poor understanding of the complexity and ecological niches of individual Group 2 subclades in saline lakes. Here, we perform comprehensive analysis of haptophyte-specific 18S rRNA sequences and distributions of LCAs, and long-chain alkenoates (LCEs) in surface sediments and suspended particulate matter (SPM) from 37 saline lakes in northern China. These lakes span a large salinity gradient from 0.5 to 308‰. Combined with published genomic data of Group 2 Isochrysidales, our phylogenetic analysis reveals three Group 2 subclades occupying distinct ecological niches: one ice-related bloomer Group 2i and two warm-season bloomers Groups 2w1 and 2w2. Group 2i, the earliest seasonal bloomer, frequently co-occurs with Group 2w1 in sediments from saline lakes with relatively low to intermediate salinity waters, whereas Group 2w2 blooms in hypersaline waters. Based on existing data, C39:4 methyl alkenone is a chemotaxonomic biomarker for Group 2i. %C37:4 (relative abundance of C37:4 to the total C37 alkenones) values in the three Group subclades follow the order: Group 2i > Group 2w2 > Group 2w1. The %C37:4 in sediment cores of saline lakes does not directly record past salinity changes, but instead reflects variable contributions in production by these three subclades. This could indirectly and partially reflect overall salinity changes in some lakes dominated by Groups 2i and 2w1, but can be more complicated in lakes dominated by other assemblages. For our sites, we also demonstrate that direct use of C37 alkenone unsaturation indices (U37K, U37K', and U37K'') for paleotemperature reconstructions in saline lakes is generally not feasible, except for cases where alkenone-producing Isochrysidales are dominated by one single species/subclade and seasonal production effects can be circumvented. We propose two possible alternative proxies for paleotemperature reconstructions in saline lakes: 1) unsaturation ratios of C41 and C42 alkenones, as these compounds are predominantly produced by a limited number of Group 2 species, such as Isochrysis nuda (Liao et al., 2020); 2) C38Et/C36OEt ratio (ratio of C38 ethyl alkenones and C36 ethyl alkenoates), which appears to have similar temperature sensitivity for Groups 2w1 and 2w2, in lakes with no Group 2i inputs. Our study provides new insights into the phylogenetic classifications of Group 2 Isochrysidales and their ecological/environmental niches, which are fundamental for more quantitative and rigorous applications of LCAs and LCEs in saline lakes as paleosalinity and paleotemperature proxies.

Southern Ocean sea surface temperature synthesis: Part 1. Evaluation of temperature proxies at glacial-interglacial time scales

Quaternary interglacial climates are often used as analogues for how the Antarctic Ice Sheet will respond to future climate warming. Southern Ocean marine sediments provide an important paleoclimate archive in this respect. Sea surface temperature (SST) reconstructions in the Southern Ocean depend exclusively on the fossils or geochemical signatures of planktic organisms, but the strengths of these SST proxies remain poorly quantified in this region. To improve confidence in paleoclimate reconstructions, Part 1 of this two-part study evaluates the reliability of Southern Ocean SST proxies employed at Quaternary glacial-interglacial time scales, focusing on three key potential problems: advection/dispersion, seasonality, and non-thermal influences. We find that foraminifera assemblages and long-chain alkenones likely provide the most reliable SST reconstructions in this region. Diatom assemblages and the Globigerina bulloides Mg/Ca ratio are considered to be ‘moderately’ reliable. Both are subject to potentially significant non-thermal influences, and diatom assemblages are likely modified by species-dependent advection as they sink to the sea floor. Nevertheless, diatoms are valuable at higher latitudes, since alkenones and foraminifera assemblages lose sensitivity below ∼1 to 2 °C. Dinocyst assemblages, radiolarian assemblages, GDGTs and Neogloboquadrina pachyderma Mg/Ca are considered the least reliable in the Southern Ocean, due to weak calibrations, poorly-constrained non-thermal influences, and/or strong advection bias. We note that the seasonality of all proxies remains poorly constrained. Overall, Southern Ocean SST reconstructions using the recommended proxies and calibrations should be robust when averaging across multiple sites and proxy types, but should be treated with caution when analysing spatial variability, a small number of sites, or a single proxy type. Quantifying the effect of advection should be a priority for all planktic groups employed in Southern Ocean paleoclimate reconstructions.

Biomarkers in the rock outcrop of the Kazusa Group reveal palaeoenvironments of the Kuroshio region

Long-chain alkenones and n-alkanes preserved in marine and lake sediment cores are widely used to reconstruct palaeoenvironments. However, applying this technique to exposed sedimentary rock sequences is relatively challenging due to the potential for the diagenetic alteration of organic biomarkers. Here, we extract long-chain alkenones and n-alkanes from an exposed outcrop of the Kazusa Group in central Japan, one of the most continuous sedimentary successions in the world, covering almost the entire Pleistocene. We find that the alkenone unsaturation ratio and average chain length of n-alkanes appears to reflect the glacial-interglacial changes in sea surface temperature and terrestrial climate, respectively. Alkenone-based sea surface temperatures between 1.1 and 1.0 million years ago concur with foraminiferal Mg/Ca-based temperature estimates and may reflect an intrusion of the Kuroshio Current. We suggest that the preservation of these biomarkers in the Kazusa Group demonstrates its potential to provide a detailed palaeoenvironmental record.