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In many palaeoceanographic studies low carbonate contents in Neogene deep-sea sediments are interpreted as dissolution events related to prominent shifts in intermediate and deep-water circulation. In the middle to late Miocene such carbonate crash events were a widespread phenomenon throughout the world's ocean basins. However, low carbonate contents may also derive from terrigenous dilution and carbonate production changes in surface waters as shown for late Miocene records of the South Atlantic ( Diester-Haass et al., 2004 , Westerhold et al., 2005 ). In order to contribute to solve this question we investigated the youngest of the Miocene crash events (10.5 Ma to 9.0 Ma) at a prominent key location of global deep water circulation, i.e. the Equatorial Atlantic Ceara Rise depth transect (ODP Sites 926, 927 and 928). By analysing different carbonate preservation proxies like carbonate content, silt grain size parameters, sand content, fragmentation index and mass accumulation rates we were able to quantify dissolution, dilution and production, and to assess previous conflicting interpretations. Critical evaluation of the different dissolution proxies and comparison to former studies revealed that silt preservation proxies do not entirely reproduce the depth dependant dissolution in the Miocene sediments, as indicated by foraminifer fragmentation. In the investigated late Miocene time slice three minima of carbonate accumulation were detected. The predominant control on these events changed from dissolution of carbonate to lowered production. The last event at 9.6 Ma is accompanied by an increased preservation but reduced carbonate accumulation. During this time the first prominent pulses of Northern Component Water (NCW) occurred, sourced most probably from the Labrador Sea. This may be understood as a first short term precursor of long time persistent and much stronger NCW production that is characteristic for younger periods and marks the turnover to the modern type of basin-to-basin fractionation between the Atlantic and Pacific. Furthermore, preservation trends of Caribbean and Ceara Rise records were in phase in contrast to former hypotheses that suggested antithetical preservation during carbonate crash events. The similarity of the preservation records in the studied ocean basins in conjunction with the inconsistency in timing of the CC-events and proposed NCW estimates indicates that changes in the carbon cycle other than dissolution controlled the CC events prior to ~ 9.9 Ma.

Records of mean sortable silt and planktonic foraminiferal preservation from the Ceara Rise (western equatorial Atlantic) and from the Caribbean are presented to analyze the Pliocene (3.5–2.2 Ma) to Pleistocene (1.6–0.3 Ma) evolution of near-bottom current strength and the carbonate corrosiveness of deep water. During the mid-Pleistocene climate transition (∼1 Ma) a drastic decrease in glacial bottom current strength and an increase in carbonate corrosiveness is registered, demonstrating a substantial decrease in the glacial contribution of the Lower North Atlantic Deep Water (LNADW) to the Atlantic Ocean. Also, an increased sensitivity to eccentricity orbital forcing is registered after the MPT. By contrast, carbonate preservation increases considerably in the deep Caribbean in response to a strong and persistent stable contribution of Upper North Atlantic Deep Water (UNADW). We found evidence for the strongest and most stable circulation within the LNADW cell during the Northern Hemisphere cooling period between ∼3.2 and 2.75 Ma. This is in agreement with the ‘superconveyor model’ which postulates that the highest NADW production took place prior to ∼2.7 Ma. A considerable decrease in bottom current strength and planktonic foraminiferal preservation is observed synchronous with the first occurrence of large-scale continental ice sheets in the Northern Hemisphere. This documents the final termination of the ‘superconveyor’ at ca. 2.75 Ma. However, our data do not support a ‘superconveyor’ in the interval between 3.5 and 3.2 Ma when high-amplitude fluctuations in bottom current flow and preservation in planktonic foraminifera are observed. Because of the great sensitivity of NADW production to changes in surface water salinity, we assume that the high-amplitude fluctuations of LNADW circulation prior to ∼3.2 Ma are linked to changes in the Atlantic salinity budget. After 2.75 Ma they are primarily controlled by ice-sheet forcing. In contrast to the stepwise deterioration of planktonic foraminiferal preservation in the western deep Atlantic, a trend toward better preservation from the Pliocene to Pleistocene is observed in the deep Caribbean. This indicates a long-term increase in the contribution of UNADW to the Atlantic Ocean.

Grain-size records of the terrigenous and calcareous silt fraction, preservation of planktic foraminifera, and benthic foraminiferal stable-isotope data (δ13C, δ18O values of C. wuellerstorfi) at ODP Site 927 on the Ceara Rise (5°27.7′N, 44°28.8′W), are used to reconstruct variations in the history of bottom current strength, ventilation, and carbonate corrosiveness of deep waters during the time interval from 0.8 to 0.3 Ma. Glacial periods are characterized by generally smaller mean sizes of the terrigenous sortable silt fraction (mean(SS)), lower δ13C values, and poorer preservation of planktic foraminifera compared to interglacials. This indicates lower bottom current speeds, larger nutrient contents and more corrosive deep water. By contrast, larger mean(SS) sizes, higher δ13C values, and well preserved planktic foraminifera indicate strong circulation and a well ventilated deep-water mass during interglacials. The observed changes are most likely related to the weakening and strengthening of circulation of Lower North Atlantic Deep Water (LNADW). Cross-spectral analysis between the mean(SS) and benthic δ18O records reveals that minima in mean(SS) occur about 7.6 k.y. after the maximum in ice volume. This indicates a considerable lag time between ice-shield induced changes in LNADW production and subsequent changes in the velocity of LNADW flow in the western equatorial Atlantic. Striking changes in bottom current speed occur regularly during glacial to interglacial transitions. Extremely fine mean(SS) minima point to an almost complete shutdown of bottom current vigor in response to a cessation of LNADW production caused by an enhanced melt water release during the initial phases of deglaciation. However, each of the fine minima extremes is followed by a rapid shift to very high mean(SS) values that indicate strong bottom currents, and hence, vigorous LNADW flow during the early interglacials. After the onset of glacial Stage 12, generally poorer carbonate preservation and higher variability is registered. This coincides with a global decrease in carbonate preservation during the mid-Brunhes (mid-Brunhes dissolution event). Detailed grain-size analysis of the calcareous fine fraction (

High-resolution benthic oxygen isotope and XRF (Fe and Ca) records from Site 1085 drilled in the Mid-Cape basin (ODP Leg 175) are used to investigate global climate changes during the Late Miocene in relation to Messinian geological events. The cyclic fluctuations of the time series at Site 1085 enable us to establish a reliable chronology for the time interval 7.3–4.7 Ma. Spectral analysis of the δ18O record indicates that the 41-kyr period of orbital obliquity dominates the Late Miocene record. A global climate record was extracted from the oxygen isotopic composition of benthic foraminifera. Both long- and short-term variabilities in the climate record are discussed in terms of sea-level and deep-water temperature changes. The time interval 7.3–6.25 Ma characterized by low-amplitude δ18O variations is followed by a period marked by maximum in the δ18O values (6.25–5.57 Ma). At about 5.56 Ma, a rapid decrease in δ18O values is documented that may reflect a warming of deep-water temperature associated with a global warming period. Comparison between the timing of the oceanic isotope events and the chronology of the Mediterranean Salinity Crisis suggest that global eustatic processes were not essential in the Mediterranean Salinity Crisis history. From our data, we infer that the global warmth documented in the Early/mid-Pliocene probably started during the Late Miocene (at 5.55 Ma). At the same time, the onset of evaporite deposition in the central basin of the Mediterranean Sea took place. Sharp changes in the sedimentation rates, mainly driven by terrigenous input at this site, are observed during the Messinian Stage.