Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/1, M34/2, M34/3 and M34/4

To enhance the limited information available about the palaeo-ecological significance of calcareous dinoflagellates, we have studied their lateral distribution in surface sediments of the equatorial and south Atlantic between 13°N and 36°S. Calcareous dinoflagellate cysts appear to be widely distributed throughout the studied area. In the surface sediments, concentrations (cyst per gram dry sediment) of the vegetative stage Thoracosphaera heimii are generally higher than that of the (presumably) calcareous resting cysts. Distribution patterns in surface sediments of Orthopithonella granifera (Fütterer) Keupp and Versteegh, Rhabdothorax spp. Kamptner., Sphaerodinella albatrosiana (Kamptner) Keupp and Versteegh S. albatrosiana praratabulated, Sphaerodinella tuberosa var. 1 (Kamptner) Keupp and Versteegh and S. tuberosa var. 2 and the ratios between these species have been compared with temperature, salinity, density and stratification gradients in the upper water column. Rhabdothorax spp. is characteristically present in sediments of more temperate regions characterized by high seasonality. Dinoflagellates producing these cysts are able to tolerate high nutrient concentrations, and mixing of the water column. S. albatrosiana is abundant in regions characterized by high sea surface temperatures and oligotrophic surface water conditions. In contrast, the distribution of S. tuberosa var. 2 is negatively related to temperature. The other cyst species did not show a characteristic pattern in relation to the studied environmental gradients. The ratio of Sphaerodinella tuberosa var. 2 to Orthopithonella granifera can be used for reconstructing the presence of stratification in the upper 50 m of the water column, whereas the ratios of S. tuberosa var. 2 to Sphaerodinella albatrosiana and of O. granifera to Rhabdothorax spp. might be used for palaeotemperature reconstructions. Calcareous dinoflagellate cysts are abundant in oligotrophic areas and may be useful for the reconstruction of palaeoenvironmental conditions.

Organic matter based proxies from surface sediments along three transects on the Pakistan continental margin

A valid assessment of selective aerobic degradation on organic matter (OM) and its impact on OM-based proxies is vital to produce accurate environmental reconstructions. However, most studies investigating these effects suffer from inherent environmental heterogeneities. In this study, we used surface samples collected along two meter-scale transects and one longer transect in the northeastern Arabian Sea to constrain initial OM heterogeneity, in order to evaluate selective aerobic degradation on temperature, productivity and alteration indices at the sediment-water interface. All of the studied alteration indices, the higher plant alkane index, alcohol preservation index, and diol oxidation index, demonstrated that they are sensitive indicators for changes in the oxygen regime. Several export production indices, a cholesterol-based stanol/stenol index and dinoflagellate lipid- and cyst-based ratios, showed significant (more than 20%) change only over the lateral oxygen gradients. Therefore, these compounds do not exclusively reflect surface water productivity, but are significantly altered after deposition. Two of the proxies, glycerol dibiphytanyl glycerol tetraether-based TEX86 sea surface temperature indices and indices based on phytol, phytane and pristane, did not show any trends related to oxygen. Nevertheless, unrealistic sea surface temperatures were obtained after application of the TEX86, TEX86L, and TEX86H proxies. The phytol-based ratios were likely affected by the sedimentary production of pristane. Our results demonstrate the selective impact of aerobic organic matter degradation on the lipid and palynomorph composition of surface sediments along a short lateral oxygen gradient and suggest that some of the investigated proxies may be useful tracers of changing redox conditions at the sediment-water interface.

Sea surface productivity and temperature detected by coccolith accumulation rates from the southeastern Pacific off Chile

Recent coccoliths from 74 surface sediment samples recovered from the southeastern Pacific off Chile were examined quantitatively to investigate modern regional gradients of sea surface productivity and temperature. All findings are based on coccolith accumulation rates. Therefore an approach was designed to estimate recent sedimentation rates based on 210Pb and bulk chemistry analyses of the same set of surface samples. Highest total coccolith accumulation rates were found off north-central Chile, where seasonal upwelling takes place. Based on amultiple linear regression between calculated coccolith accumulation rates andWorld Ocean Atlas derived sea surface temperatures, a calibrationmodel to reconstruct annual average temperatures of the uppermost 75 mof thewater column is provided. Themodelwas cross-validated and the SST estimateswere compared with SST observed and SST estimates based on diatoms and planktonic foraminifera, showing a good correlation.

Sea surface temperature calculation based on alkenones in sediments off northwest Africa

The molecular stratigraphy of Biogeochemical Oceanic Flux Study core 31K (19°N, 20°10'W) and Ocean Drilling Program Hole 658C (20°45'N, 18°35'W) has been studied for C37 alkenone abundances over the past 80 ka at high resolution (~circa 200-500 years). The derived Uk 37' sea surface temperature record for both cores shows a range of temperatures from about 18°C during the last glacial to 21.5°C during the early Holocene. Both records also reveal changes in sea surface temperature as much as 2°-4°C over a few hundred years, which correlate well with similar abrupt climatic changes observed in cores from elsewhere in the NE Atlantic, associated with 'Heinrich events'. Our results indicate that meltwater produced by these ice-rafting events was transmitted southward by the Canary Current, where it had considerable impact on sea surface temperatures in the subtropical eastern Atlantic.

Sea-surface temperature reconstructions for the Quaternary western Atlantic

Paleotemperature estimates calculated by the SIMMAX Modern Analog Technique are presented for two gravity cores from the Rio Grande Rise, one from the Brazil Slope, and one from the Ceara Rise. The estimates are based on comparisons between modern and fossil planktonic foraminiferal assemblages and were carried out on samples from Quaternary sediments. Estimated warm-season temperatures from the Rio Grande Rise (at approx. 30° S) range from around 19°C to 24°C, with some coincidence of warm peaks with interglacial stages. The temperature estimates (also warm-season) from the more tropical Brazil Slope (at approx. 8° S) and Ceara Rise (at approx. 4° N) cores are more stable, remaining between 26°C and 28°C throughout most of their lengths. This fairly stable situation in the tropical western Atlantic is interrupted in oxygen isotope stage 6 by a significant drop of 2-3°C in both of these cores. Temperature estimates from the uppermost samples in all cores compare very well to the modern-day measured values. Affinities of some foraminiferal species for warmer or cooler surface temperatures are identified within the temperature range of the examined samples based on their abundance values. Especially notable among the warmer species are, Globorotalia menardii, Globigerinita glutinata, Globigerinoides ruber, and Globigerinoides sacculifer. Species indicative of cooler surface temperatures include Globorotalia inflata, Globigerina bulloides, Neogloboquadrina pachyderma, and Globigerina falconensis. A cluster analysis was carried out to assist in understanding the degree of variation which occurs in the foraminiferal assemblages, and how temperature differences influence the faunal compositions of the samples. It is demonstrated that fairly similar samples may have unexpectedly different estimated temperatures due to small differences in key species and, conversely, quite different assemblages can result in similar or identical temperature estimates which confirms that other parameters than just temperature affect faunal content.

Sea surface temperature and stable isotopes from 9 cores of the Northeastern Atlantic

Temporal and spatial patterns in eastern North Atlantic sea-surface temperatures (SST) were reconstructed for marine isotope stage (MIS) 11c using a submeridional transect of five sediment cores. The SST reconstructions are based on planktic foraminiferal abundances and alkenone indices, and are supported by benthic and planktic stable isotope measurements, as well as by ice-rafted debris content in polar and middle latitudes. Additionally, the larger-scale dynamics of the precipitation regime over northern Africa and the western Mediterranean region was evaluated from iron concentrations in marine sediments off NW Africa and planktic d13C in combination with analysis of planktic foraminiferal abundances down to the species level in the Mediterranean Sea. Compared to the modern situation, it is revealed that during entire MIS 11c sensu stricto (ss), i.e., between 420 and 398 ka according to our age models, a cold SST anomaly in the Nordic seas co-existed with a warm SST anomaly in the middle latitudes and the subtropics, resulting in steeper meridional SST gradients than during the Holocene. Such a SST pattern correlates well with a prevalence of a negative mode of the modern North Atlantic Oscillation. We suggest that our scenario might partly explain the longer duration of wet conditions in the northern Africa during MIS 11c compared to the Holocene.

(Table 1) Sea surface temperature reconstruction for eastern equatorial Pacific surface sediment samples

Significant uncertainties persist in the reconstruction of past sea surface temperatures in the eastern equatorial Pacific, especially regarding the amplitude of the glacial cooling and the details of the post-glacial warming. Here we present the first regional calibration of alkenone unsaturation in surface sediments versus mean annual sea surface temperatures (maSST). Based on 81 new and 48 previously published data points, it is shown that open ocean samples conform to established global regressions of Uk'37 versus maSST and that there is no systematic bias from seasonality in the production or export of alkenones, or from surface ocean nutrient concentrations or salinity. The flattening of the regression at the highest maSSTs is found to be statistically insignificant. For the near-coastal Peru upwelling zone between 11-15°S and 76-79°W, however, we corroborate earlier observations that Uk'37 SST estimates significantly over-estimate maSSTs at many sites. We posit that this is caused either by uncertainties in the determination of maSSTs in this highly dynamic environment, or by biasing of the alkenone paleothermometer toward El Niño events as postulated by Rein et al. (2005).

(Table 2) Dinoflagellate cysts in surface sediment samples of METEOR cruises M20/2, M23/1, M34/2 and M34/2

The organic walled cyst content of 41 surface sediment samples from the south-eastern South Atlantic Ocean have been studied to create a dataset that can be used for palaeoceanographic reconstructions. In order to obtain insight into which environmental factors influence the distribution of individual cyst species, the cyst associations have been compared with oceanographic characteristics of the overlying water masses, i.e. temperature, salinity, density and stratification gradients. The associations and relationships have been established by visual examination of the dataset and the multivariate ordination techniques, Detrended Correspondence Analysis and Canonical Correspondence Analysis. Special attention has been given to the factors of transport and preservation of the cysts. Five associations have been recognised as being characteristic of (1) areas influenced by coastal upwelling and/or river outflow, (2) open ocean, (3) Agulhas Current and southern Benguela Current, (4) Benguela Current and (5) Walvis Bay, shelf break area. The factors dominant in influencing either directly or indirectly the cyst distributions appear to be the stratification in the upper 50 m of the water column, nutrient concentration and seasonality. Variations in sea surface temperatures and salinities have only minor effect on cyst distribution.

Sea-surface paleotemperature reconstructions for the middle Miocene-Holocene of ODP Site 133-811 in the Coral Sea off northeast Australia

The derivation of a detailed sea-surface paleotemperature curve for the middle Miocene-Holocene (10-0 Ma) from ODP Site 811 on the Queensland Plateau, northeast Australia, has clarified the role of sea-surface temperature fluctuations as a control on the initiation and development of the extensive carbonate platforms of this region. This curve was derived from isotopic analyses of the planktonic foraminifer Globigerinoides ruber, and converted to temperature using the surface-water paleotemperature equation accounting for variations in global ice volume. The accuracy of these data were confirmed by derivation of paleotemperatures using the water column isotopic gradient (Delta delta18O), corrected for salinity and variations in seafloor water mass temperature. Results indicate that during this period surface-water temperatures were, on average, greater than the minimum required for tropical reef growth (20°C; Veron, 1986), with the exception of the late Miocene and earliest early Pliocene (10-4.9 Ma), when there were repeated intervals of temperatures between 18-20°C. Tropical reef growth on the Queensland Plateau was extensive from the early to early middle Miocene (~21-13 Ma), after which reef development began to decline. A lowstand near 11 Ma probably exposed shallower portions of the plateau; after re-immersion near 7 Ma, the areal extent of reef development was greatly reduced (~ 50%). Paleotemperature data from Site 811 indicate that decreased sea-surface temperatures were likely to have been instrumental in reducing the area of active reef growth on the Queensland Plateau. Reduced reefal growth rates continued until the late Pliocene or Quaternary, despite the increase of average sea-surface paleotemperatures to 22-23°C. Studies on modern corals show that when sea-surface temperatures are below ~24°C, as they were from the late Miocene to the Pleistocene off northeast Australia, corals are stressed and growth rates are greatly reduced. Consequently, when temperatures are in this range, corals have difficulty keeping pace with subsidence and changing environmental factors. In the late Pliocene, sedimentation rates increased due to increases in non-reefal carbonate production and falling sea levels. It was not until the mid-Quaternary (0.6-0.7 Ma) that sea-surface paleotemperatures increased above 24°C as a result of the formation of a western Coral Sea warm water pool. Because of age discrepancies, it is unclear exactly when an effective barrier developed on the central Great Barrier Reef; the formation of the warm water pool was likely to have either assisted the formation of this barrier and/or permitted increased coral growth rates. Fluctuations in sea-surface temperature can account for much of the observed spatial and temporal variations of reef growth and carbonate platform distribution off northeast Australia, and therefore we conclude that paleotemperature variations are a critical control on the development of carbonate platforms, and must be considered an important cause of ancient platform "drowning".

Sea surface temperature variations recorded on coralline Sr/Ca ratios during Mid-Late Holocene in Leizhou Peninsula

High-resolution Sr/Ca ratios of two Porites corals from Leizhou Peninsula were measured using inductively coupled plasma atomic spectrometry (ICP-AES). TIMS U-Th dating reveals that the life-spans of the two corals are 489500 AD and 539-530 BC, respectively. Monthly sea surface temperatures (SSTs) during these two periods can be reconstructed from their skeletal Sr/Ca ratios. The results reveal that SSTs during 539-530 BC were roughly the same as those during 1990-2000 AD in this area, indicating a relative warm climate period. However, the period of 489-500 AD was significantly cooler, with annual mean SST, the 10-a average of minimum monthly winter SSTs and the 10-a average of maximum monthly summer SSTs being about 2, 2.9 and 1degreesC lower than that in the 1990s, respectively. Such climate patterns agree well with the phenological results recorded in the historic documents in other areas of China.

Water temperature reconstructions based on paired Uk'37 and Tex86 records, and paired surface and subsurface Mg/Ca records

This dataset contains the collection of available published paired Uk'37 and Tex86 records spanning multi-millennial to multi-million year time scales, as well as a collection of Mg/Ca-derived temperatures measured in parallel on surface and subsurface dwelling foraminifera, both used in the analyses of Ho and Laepple, Nature Geoscience 2016. As the signal-to-noise ratios of proxy-derived Holocene temperatures are relatively low, we selected records that contain at least the last deglaciation (oldest sample >18kyr BP).

Glacial North Atlantic: Sea surface conditions reconstructed by GLAMAP 2000

The response of the tropical ocean to global climate change and the extent of sea ice in the glacial nordic seas belong to the great controversies in paleoclimatology. Our new reconstruction of peak glacial sea surface temperatures (SSTs) in the Atlantic is based on census counts of planktic foraminifera, using the Maximum Similarity Technique Version 28 (SIMMAX-28) modern analog technique with 947 modern analog samples and 119 well-dated sediment cores. Our study compares two slightly different scenarios of the Last Glacial Maximum (LGM), the Environmental Processes of the Ice Age: Land, Oceans, Glaciers (EPILOG), and Glacial Atlantic Ocean Mapping (GLAMAP 2000) time slices. The comparison shows that the maximum LGM cooling in the Southern Hemisphere slightly preceeded that in the north. In both time slices sea ice was restricted to the north western margin of the nordic seas during glacial northern summer, while the central and eastern parts were ice-free. During northern glacial winter, sea ice advanced to the south of Iceland and Faeroe. In the central northern North Atlantic an anticyclonic gyre formed between 45° and 60°N, with a cool water mass centered west of Ireland, where glacial cooling reached a maximum of >12°C. In the subtropical ocean gyres the new reconstruction supports the glacial-to-interglacial stability of SST as shown by CLIMAP Project Members (CLIMAP) [1981]. The zonal belt of minimum SST seasonality between 2° and 6°N suggests that the LGM caloric equator occupied the same latitude as today. In contrast to the CLIMAP reconstruction, the glacial cooling of the tropical east Atlantic upwelling belt reached up to 6°-8°C during Northern Hemisphere summer. Differences between these SIMMAX-based and published U37[k]- and Mg/Ca-based equatorial SST records are ascribed to strong SST seasonalities and SST signals that were produced by different planktic species groups during different seasons.