Sea surface temperatures during Marine Isotope Stage (MIS) 11

The Marine Isotope Stage (MIS) 11 (424-374 ka) was characterized by a protracted deglaciation and an unusually long climatic optimum. It remains unclear to what degree the climate development during this interglacial reflects the unusually weak orbital forcing or greenhouse gas trends. Previously, arguments about the duration and timing of the MIS11 climatic optimum and about the pace of the deglacial warming were based on a small number of key records, which appear to show regional differences. In order to obtain a global signal of climate evolution during MIS11, we compiled a database of 78 sea surface temperature (SST) records from 57 sites spanning MIS11, aligned these individually on the basis of benthic (N = 28) or planktonic (N = 31) stable oxygen isotope curves to a common time frame and subjected 48 of them to an empirical orthogonal function (EOF) analysis. The analysis revealed a high commonality among all records, with the principal SST trend explaining almost 49% of the variability. This trend indicates that on the global scale, the surface ocean underwent rapid deglacial warming during Termination V, in pace with carbon dioxide rise, followed by a broad SST optimum centered at ~410 kyr. The second EOF, which explained ~18% of the variability, revealed the existence of a different SST trend, characterized by a delayed onset of the temperature optimum during MIS11 at ~398 kyr, followed by a prolonged warm period lasting beyond 380 kyr. This trend is most consistently manifested in the mid-latitude North Atlantic and Mediterranean Sea and is here attributed to the strength of the Atlantic meridional overturning circulation. A sensitivity analysis indicates that these results are robust to record selection and to age-model uncertainties of up to 3-6 kyr, but more sensitive to SST seasonal attribution and SST uncertainties >1 °C. In order to validate the CCSM3 (Community Climate System Model, version 3) predictive potential, the annual and seasonal SST anomalies recorded in a total of 74 proxy records were compared with runs for three time slices representing orbital configuration extremes during the peak interglacial of MIS11. The modeled SST anomalies are characterized by a significantly lower variance compared to the reconstructions. Nevertheless, significant correlations between proxy and model data are found in comparisons on the seasonal basis, indicating that the model captures part of the long-term variability induced by astronomical forcing, which appears to have left a detectable signature in SST trends.

Eocene-Oligocene nannofossils from the Labrador Sea

During Ocean Drilling Program (ODP) Leg 105, a thick sequence of lower Eocene to lower Oligocene sediments was recovered from Hole 647A in the southern Labrador Sea. These sediments contain diverse, well-preserved, high-latitude calcareous nannofossil flora. The nannofossil biostratigraphy of the hole indicates the presence of a minor hiatus between Zones NP 16 and NP 17 in the upper middle Eocene and a barren interval separating Zones NP 13 and NP 15. Species abundance is highest within the lower to middle Eocene and starts to decline near the base of the upper Eocene. No major change in the nannoflora was observed across the Eocene/Oligocene boundary, although a slight decrease in species abundance was recorded. The Paleogene calcareous nannofossils of nearby DSDP Site 112 were reexamined and compared with those of Site 647. Several cores were reassigned to different nannofossil zones. The calcareous nannoflora are dominated by high-latitude indicative species and also exhibit a high diversity, which suggests the influence of more temperate water masses in this region during Eocene and Oligocene time. One new subspecies from the middle Eocene, Sphenolithus furcatolithoides labradorensis, is described.

(Table 1) Compressional wave velocities for rocks from DSDP Hole 31-293 in the Philippine Sea

Compressional wave velocities measured in gabbroic rocks and metabasites recovered from Site 293 of Leg 31 in the Philippine Sea (on the Central Basin Fault) are correlative with seismic velocities determined for Layer 3. The lower crustal origin for these rocks suggested by this data is further supported by the similarity between these samples, dredge haul samples from fracture zones in the main ocean basins and rocks found in ophiolite complexes. These plutonic rocks were possibly introduced to the sea floor by movements along the Central Basin Fault, a major tectonic feature in the Philippine Sea, or formed as part of new ocean crust within a leaky transform fault.

Quaternary isotope stratigraphy of DSDP Hole 90-593 from the Challenegr Plateau, South Tasman Sea

A moderate-resolution isotope stratigraphy (with an average of one sample per 17,500 yr.) derived from the benthic foraminifer Uvigerina (or Cibicides), the planktonic foraminifer Globigerina bulloides, and calcareous nannofossil concentrates is presented for the entire Quaternary (and latest Pliocene) section of mid-upper bathyal calcareous oozes from DSDP Site 593, western Challenger Plateau, south Tasman Sea. Superimposed on a trend of gradually increasing average delta18O values through the Pleistocene, reflecting the progressive buildup of polar ice sheets, is a record of highfrequency but generally low amplitude (0.5-1?) isotope fluctuations in the early Quaternary (1.9-1.0 m.y.), followed by a greatly increased intensity (1.5-2.0 ?) of glacial-interglacial fluctuations during the late Quaternary (< 1.0 m.y.). The standard late Quaternary isotope stages 1 to 24 are mainly resolvable. Significant excursions in both delta18O and delta13C values at various times during the Quaternary are suggested to be due to periodic, fundamental changes in ocean circulation properties over the plateau. For example, intensified upwelling of Antarctic Intermediate Waters during several glacial periods is indicated by the convergence of benthic and planktonic foraminiferal delta18O data, and productivity variations may account for certain delta13C spikes in the record. With increasingly higher resolution analysis this core will provide a useful Quaternary isotope reference section for southern temperate waters in the southwest Pacific, centered on New Zealand.

Distribution of Cycladophora davisiana davisiana in upper Pliocene and Pleistocene sediments of the North Atlantic and Labrador Sea

Upper Pliocene and Pleistocene abundance fluctuations of the radiolarian Cycladophora davisiana (Ehrenberg) davisiana (Petrushevskaya) are documented from North Atlantic (Site 609) and Labrador Sea (Site 646B) to provide the first long-term correlation of its abundance fluctuations to oxygen isotope stages 1-114. Also examined are temporal and regional fluctuations in abundances C. d. davisiana and the global dispersal routes of the species. The first occurrence of C. d. davisiana in the eastern North Atlantic Ocean (Site 609) occurred between 2.586 and 2.435 Ma (oxygen isotope stages 109.66-102.19). During the early Matuyama Chron, prior to oxygen isotope stage 63, C. d. davisiana abundances were less than 1% and never greater than 12%, while abundances of greater than 5% are found in stages 65.71-73, 74, and 83-84. The initial major abundance peak (35.7%) of C. d. davisiana was noted near the stage 63/62 boundary. Abundance peaks of greater than 15%, between oxygen isotope stages 35 and 63, are limited to stages 63.02, 58.07, 55.07-54.26, and 50.76-50.22. These represent the only such abundance peaks detected during the first c. 1.5 million years of the species within the North Atlantic. The character of C. d. davisiana abundance fluctuations in Site 609 changes after oxygen isotope stage 35; average abundances are greater (7.7% vs. 4.3%) and abundance maxima of more than 15% are more frequent. Many, but not all, peak abundances of C. d. davisiana occur in glacial stages (e.g., 8, 14, 18, 20, 26, 30, 34, 50, 54, and 58). Increased abundances of the species are also noted in weak interglacial stages (e.g., stages 3, 23, 39, and 41), and significant cool periods of robust interglacial periods (e.g., late stage 11). Sample spacing is adequate in some stages to note some rapid changes in abundance near stage transitions (e.g., stages 4/5, 25/26, 62/63). The sample density in Holes 609 and 611 and the upper portion of 646B is sufficient to detect a synchroneity of many abundance maxima and minima among sites. Some abundance peaks are undetected in one or more of the two holes, warranting further sampling to obtain a more accurate record of regional abundance fluctuations. Prior to stage 36, few ages of Hole 611 peaks are the same as those in the more precisely dated Hole 609. The highest abundances of C. d. davisiana were noted in Labrador Sea Hole 646B where the earliest known occurrence of the species is documented (3.08-2.99 Ma). C. d. davisiana is inferred to have evolved in the Labrador Sea (or Arctic), and migrated next through the Arctic into the North Pacific (2.62-2.64 Ma, stage 114) before migrating into the Norwegian Sea (2.63-2.53 Ma) and North Atlantic (2.59-2.44 Ma, stages 109-102). Additional migration of C. d. dauisiana into the southern South Atlantic (Site 704) occurred much later (2.06 Ma, stage 83).

Sea surface temperature reconstruction based on dinoflagellates from the North Atlantic

The application of quantitative and semiquantitative methods to assemblage data from dinoflagellate cysts shows potential for interpreting past environments, both in terms of paleotemperature estimates and in recognizing water masses and circulation patterns. Estimates of winter sea-surface temperature (WSST) were produced by using the Impagidinium Index (II) method, and by applying a winter-temperature transfer function (TFw). Estimates of summer sea-surface temperature (SSST) were produced by using a summer-temperature transfer function (TFs), two methods based on a temperature-distribution chart (ACT and ACTpo), and a method based on the ratio of gonyaulacoid:protoperidinioid specimens (G:P). WSST estimates from the II and TFw methods are in close agreement except where Impagidinium species are sparse. SSST estimates from TFs are more variable. The value of the G:P ratio for the Pliocene data in this paper is limited by the apparent sparsity of protoperidinioids, which results in monotonous SSST estimates of 14-26°C. The ACT methods show two biases for the Pliocene data set: taxonomic substitution may force 'matches' yielding incorrect temperature estimates, and the method is highly sensitive to the end-points of species distributions. Dinocyst assemblage data were applied to reconstruct Pliocene sea-surface temperatures between 3.5-2.5 Ma from DSDP Hole 552A, and ODP Holes 646B and 642B, which are presently located beneath cold and cool-temperate waters north of 56°N. Our initial results suggest that at 3.0 Ma, WSSTs were a few degrees C warmer than the present and that there was a somewhat reduced north-south temperature gradient. For all three sites, it is likely that SSSTs were also warmer, but by an unknown, perhaps large, amount. Past oceanic circulation in the North Atlantic was probably different from the present.

Composition of Quaternary and Neogene-Quaternary sedimentary rocks from the Black Sea

Processes of sedimentation in marine basins locating in the area of interaction of the largest continental plates (African and Eurasian) are under consideration in the book. During the giant tectonic reconstruction of the Tethys Ocean semi-enclosed seas - the Mediterranean and Black originated. Their sedimentary sequence contains a recording of complex history of the Alpine-Himalayan belt. The dramatic history of the seas and their feeding catchments during Cenozoic is described in detail on the base of unique material of coring and deep-sea drilling, as well as a variety of geophysical and geochemical studies. Particular attention is paid to the history of volcanism - terrestrial and underwater - with correlation of ash falls accumulated on the land and in marine sediments.

Response of nannoplankton to major changes in sea-surface temperature at the South Chatham Rise, southeastern New Zealand

A high-resolution history of paleoceanographic changes in the subpolar waters of the southern margin of the Subtropical Convergence Zone during the last 130 kyr, is present in foraminiferal assemblages of DSDP Site 594. The foraminifera indicate that sea-surface temperatures during the Last Interglacial Climax were warmer than today, and that between substage 5d through to the end of isotope stage 2, temperatures were mostly cooler than Holocene temperatures. The paleotemperatures suggest that (1) the Subtropical Convergence was located over the site during substage 5e, later moving further north, then moving southwards to near the site during the Holocene, and (2) the Polar Front was positioned over the Site during glacial stages 6, 4, 2 and possibly parts of stage 3. Several major events are indicated by the nannofloral assemblages during these large changes in sea-surface temperature and associated reorganization of ocean circulation. First, the time-progressive trends between E. huxleyi and medium to large Gephyrocupsa are unique to this site, with E. huxleyi dominating over medium Gephyrocupsa during stages 5c-a, middle part of stage 4 and after the middle point of stage 3. This unusual trend may (at least partly) be caused by the shift of the Polar Front across the site. Second, upwelling flora (E. huxleyi and small placoliths) increase in abundance during stages 1, 3 and 5, suggesting that upwelling or disturbance of water stratification took place during the interglacials. Thirdly, there are no significant differences between the distribution patterns of the various morphotypes of medium to large Gephyrocupsu, and the combined value of all medium Gephyrocupsu increases in abundance during glacials (stages 2 and 4 and the end of stage 6), similar to the abundance trends in benthic foraminifera. Finally, subordinate nannofossil taxa also show distinctive climatic trends during the last glacial cycle: (1) Syrucosphaera spp. are present in increased abundance during warmer extremes in climate (substages 5e, 5a, and stage 1); (2) Coccolithus pelagicus and Culcidiscus leptoporus dominate the subordinate nannofossil taxa, and their relative proportions seem to provide a useful paleoceanographic index, with C. pelagicus dominating when the Polar Front Zone is over the site (stages 6, 4 and 2), whilst C. leptoporus is relatively more abundant when the STC is positioned over the site (stages 1 and 5e). Increased abundance of C. pelagicus also can indicate intensified coastal upwelling.

Geochemistry of evaporite in the Red Sea

One of the major shipboard findings during Leg 23 drilling in the Red Sea was the presence of late Miocene evaporites at Sites 225, 227, and 228. The top of the evaporite sequence correlates with a strong reflector (Reflector S) which has been mapped over much of the Red Sea (Ross et al., 1969, Phillips and Ross, 1970). This indicates that the Red Sea appears to be extent. Miocene sediments, including evaporites, are known from a few outcrops along the coastal plains of the Gulf of Suez to lat 14°N (Sadek, 1959, cited in Friedman, 1972; Heybroek, 1965; Friedman, 1972). Along the length of the Red Sea, the presence of Miocene salt is indicated by seismic reflection studies (Lowell and Genik, 1972) and confirmed by drilling. The recently published data from deep exploratory wells (Ahmed, 1972) demonstrate the great thickness of elastics and evaporites which were deposited in the Red Sea depression during Miocene time. The Red Sea evaporites are of the same age as the evaporites found by deep sea drilling (DSDP Leg 13) in the Mediterranean Sea. Therefore, Reflector S in the Red Sea is comparable to Reflector M in the Mediterranean. It is assumed that during Miocene time a connection between these two basins was established (Coleman, this volume) resulting in a similar origin for the evaporites deposited in the Red Sea and in the Mediterranean Sea. The origin of the Mediterranean evaporites has been discussed in great detail (Hsü et al., 1973; Nesteroff, 1973; Friedman, 1973). The formation of evaporites may be interpreted by three different hypotheses. 1) Evaporation of a shallow restricted shelf sea or lagoon which receives inflows from the open ocean. 2) Evaporation of a deep-water basin which is separated from the open ocean by a shallow sill (Schmalz, 1969). 3) Evaporation of playas or salt lakes which are situated in desiccated deep basins isolated from the open ocean (Hsü et al., 1973). The purpose of this study is to show whether one of these models might apply to the formation and deposition of the Red Sea evaporites. Therefore, a detailed petrographic and geochemical investigation was carried out.

Early Maastrichtian stable isotopes: changing deep water sources in the North Atlantic?

We propose that the observed short-term stable isotope fluctuations reflect changes in high- and low-latitude intermediate to deep water sources, based on a high-resolution stable isotope record of planktic and benthic foraminifera from the Early Maastrichtian (~71.3 to ~ 69.6 Ma) of Blake Nose (DSDP Site 390A, North Atlantic). Sources of these waters may have been the low-latitude eastern Tethys and high-latitude North Atlantic. Changes in intermediate to deep water sources were probably steered by eccentricity-controlled insolation fluctuations. Lower insolation favored the formation of high-latitude deep waters due to positive feedback mechanisms resulting in high-latitude cooling. This led to a displacement of low-latitude deep waters at Blake Nose. Higher insolation reduced intermediate to deep-water formation in high latitudes, yielding a more northern flow of low-latitude deep waters.

Rare and trace element analyses from DSDP Holes 31-291 and 31-294 from the Philippine Sea

Metal-rich sediments were found in the West Philippine Basin at DSDP sites 291 (located about 500 km SW of the Philippine Ridge or Central Basin Fault) and 294/295 (located about 580 km NE of the Philippine Ridge). In both cases the metalliferous deposits constitute a layer, probably Eocene in age, resting directly above the basaltic basement at the bottom of the sediment column. The chemistry of the major (including Fe and Mn) and trace elements (including trace metals, rare earth elements, U and Th) suggest a strong similarity of these deposits to metalliferous deposits produced by hydrothermal activity at oceanic spreading centers. Well-crystallized hematite is a major component of the metal-rich deposits at site 294/295. We infer that the Philippine Sea deposits were formed at some spreading center by hydrothermal processes of metallogenesis, similar to processes occurring at oceanic spreading centers. A locus for their formation might have been the Philippine Ridge (Central Basin Fault), probably an extinct spreading center. We conclude that metallogenesis of the type occurring at oceanic spreading centers can take place also in marginal basins. This has implications for the origin of metal deposits found in some ophiolite complexes, such as those in Luzon (Philippines), which may represent fragments of former marginal basins rather than of oceanic lithosphere.

Rhenium and platinum-group element concentrations and Os isotope data for Philippine Sea Plate basalts from DSDP Legs 31, 58, and 59

Platinum-group elements (PGE), rhenium and osmium isotope data are reported for basalts from Deep Sea Drilling Project cores in the Philippine Sea Plate (PSP). Lithophile trace element and isotopic characteristics indicate a range of source components including DMM, EMII and subduction-enriched mantle. MORB-like basalts possess smooth, inclined chondrite-normalised PGE patterns with high palladium-PGE/iridium-PGE ratios, consistent with previously published data for MORB, and with the inferred compatibility of PGE. In contrast, while basalts with EMII-type lithophile element chemistry possess high Pt/Ir ratios, many have much lower Pd/Ir and unusually high Ru/Ir of >10. Similarly, back-arc samples from the Shikoku and Parece-Vela basins have very high Ru/Ir ratios (>30) and Pd/Ir as low as 1.1. Such extreme Pd/Ir and Ru/Ir ratios have not been previously reported in mafic volcanic suites and cannot be easily explained by variable degrees of melting, fractional crystallisation or by a shallow-level process such as alteration or degassing. The data appear most consistent with sampling of at least two mantle components with distinct PGE compositions. Peridotites with the required PGE characteristics (i.e. low Pd, but relatively high Ru and Re) have not been documented in oceanic mantle, but have been found in sub-continental mantle lithosphere and are the result of considerable melt depletion and selective metasomatic enrichment (mainly Re). The long-term presence of subduction zones surrounding the Philippine Sea Plate makes this a prime location for metasomatic enrichment of mantle, either through fluid enrichment or infiltration by small melt fractions. The Re-Os isotope data are difficult to interpret with confidence due to low Os concentrations in most samples and the uncertainty in sample age. Data for Site 444A (Shikoku Basin) give an age of 17.7+/-1.3 Ma (MSWD = 14), consistent with the proposed age of basement at the site and thus provides the first robust radiometric age for these samples. The initial 187Os/188Os of 0.1298+/-0.0069 is consistent with global MORB, and precludes significant metasomatic enrichment of Os by radiogenic slab fluids. Re-Os data for Sites 446A (two suites, Daito Basin) and 450 (Parece-Vela Basin) indicate ages of 73, 68 and 43 Ma, which are respectively, 30, 17 and >12 Ma older than previously proposed ages. The alkalic and tholeiitic suites from Site 446A define regression lines with different 187Os/188Osinitial (0.170+/-0.033 and 0.112+/-0.024, respectively) which could perhaps be explained by preferential sampling of interstitial, metasomatic sulphides (with higher time-integrated Re/Os ratios) by smaller percentage alkalic melts. One sample, with lithophile elements indistinguishable from MORB, is Os-rich (146 pg/g) and has an initial 187Os/188Os of 0.1594, which is at the upper limit of the accepted OIB range. Given the Os-rich nature of this sample and the lack of evidence for subduction or recycled crust inputs, this osmium isotope ratio likely reflects heterogeneity in the DMM. The dataset as a whole is a striking indication of the possible PGE and Os isotope variability within a region of mantle that has experienced a complex tectonic history.

(Table 1) Sea-surface temperatures, intermediate-water temperatures, and latitudinal gradient at three time slices at the end of the Cretaceous

Climatic and oceanographic variations during the last 2 m.y. of the Maastrichtian inferred from high-resolution (10 k.y.) stable isotope analysis of the mid-latitude South Atlantic Deep Sea Drilling Project Site 525 reveal a major warm pulse followed by rapid cooling prior to the Cretaceous-Tertiary boundary. Between 66.85 and 65.52 Ma, cool but fluctuating temperatures average 9.9 and 15.4°C in intermediate and surface waters, respectively. This interval is followed by an abrupt short-term warming between 65.45 and 65.11 Ma, which increased temperatures by 2-3°C in intermediate waters, and decreased the vertical thermal gradient to an average of 2.7°C. This warm pulse may be linked to increased atmospheric pCO2, increased poleward heat transport, and the switch of an intermediate water source from high to low-middle latitudes. During the last 100 k.y. of the Maastrichtian, intermediate and surface temperatures decreased by an average of 2.1 and 1.4°C, respectively, compared to the maximum temperature between 65.32 and 65.24 Ma.