Evolution of millennial-scale climate variability during the mid-Pleistocene (original) (raw)
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Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic d 18 O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 ($940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic d 18 O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic d 18 O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.
Paleoceanography, 2012
Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic d 18 O time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 ($940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic d 18 O time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic d 18 O) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator.
Millennial-scale climate variability in the subpolar North Atlantic Ocean during the late Pliocene
Paleoceanography, 2010
1] Large-amplitude millennial-scale climate oscillations have been identified in late Pleistocene climate archives from around the world. These oscillations appear to be of larger amplitude during times of enlarged ice sheets. This observation suggests the existence of a relationship between large-amplitude millennial variations in climate and extreme glacial conditions and therefore that the emergence of millennial-scale climate variability may be linked to the Pliocene intensification of northern hemisphere glaciation (iNHG). Here we test this hypothesis using new late Pliocene high-resolution (∼400 year) records of ice-rafted debris deposition and stable isotopes in planktic foraminiferal calcite (Globigerinoides ruber) generated from Integrated Ocean Drilling Program Site U1313 in the subpolar North Atlantic (a reoccupation of the classic Deep Sea Drilling Project Site 607). Our records span marine oxygen isotope stages (MIS) 103-95 (∼2600 to 2400 ka), the first interval during iNHG (∼3.5 to 2.5 Ma) in which large-amplitude glacial-interglacial cycles and inferred sea level changes occur. Our records reveal small-amplitude variability at periodicities of ∼1.8 to 6.2 kyr that prevails regardless of (inter)glacial state with no significant amplification during the glacials MIS 100, 98, and 96. These findings imply that the threshold for the amplification of such variability to the proportions seen in the marine archive of the last glacial was not crossed during the late Pliocene and, in view of all available data, likely not until the Mid-Pleistocene Transition.
Quaternary Science Reviews, 2011
Stable carbon and oxygen isotopes from benthic and planktic foraminifers, planktic foraminifer assemblages and ice rafted debris from the North Atlantic Site U1314 (Integrated Ocean Drilling Program Expedition 306) were examined to investigate orbital and millennial-scale climate variability in the North Atlantic and its impact on global circulation focusing on the development of glacial periods during the mid-Pleistocene (ca 800e400 ka). Glacial initiations were characterized by a rapid cooling (6e10 C in less than 7 kyr) in the mean annual sea surface temperature (SST), increasing benthic d 18 O values and high benthic d 13 C values. The continuous increase in benthic d 18 O suggests a continuous ice sheet growth whereas the positive benthic d 13 C values indicate that the flow of the Iceland Scotland Overflow water (ISOW) was vigorous. Strong deep water formation in the Norwegian Greenland Sea promoted a high transfer of freshwater from the ocean to the continents. However, low SSTs at Site U1314 suggest a subpolar gyre cooling and freshening that may have reduced deep water formation in the Labrador Sea during glacial initiations. Once the 3.5& threshold in the benthic d 18 O record was exceeded, ice rafting started and ice sheet growth was punctuated by millennial-scale waning events which returned to the ocean part of the freshwater accumulated on the continents. Ice-rafting events were associated with a rapid reduction in the ISOW (benthic d 13 C values dropped 0.5e1&) and followed by millennial-scale warmings. The first two millennial-scale warm intervals of each glacial period reached interglacial temperatures and were particularly abrupt (6e10 C in w3 kyr). Subsequent millennial-scale warm events were cooler probably because the AMOC was rather reduced as suggested by the low benthic d 13 C values. These two abrupt warming events that occurred at early glacial periods were also observed in the Antarctic temperature and CO 2 records, suggesting a close correlation between both Hemispheres. The comparison of the sea surface proxies with the benthic d 18 O record (as the Southern sign) indicates the presence of a millennial-scale seesaw pattern similar to that seen during the Last Glacial period.
Earth and Planetary Science Letters, 2010
The Mid-Pleistocene transition (MPT) was the time when quasi-periodic (∼ 100 kyr), high-amplitude glacial variability developed in the absence of any significant change in the character of orbital forcing, leading to the establishment of the characteristic pattern of late Pleistocene climate variability. It has long been known that the interval around 900 ka stands out as a critical point of the MPT, when major glaciations started occurring most notably in the northern hemisphere. Here we examine the record of climatic conditions during this significant interval, using high-resolution stable isotope records from benthic and planktonic foraminifera from a sediment core in the North Atlantic (Integrated Ocean Drilling Program Expedition 306, Site U1313). We have considered the time interval from late in Marine Isotope Stage (MIS) 23 to MIS 20 (910 to 790 ka). Our data indicate that interglacial MIS 21 was a climatically unstable period and was broken into four interstadial periods, which have been identified and correlated across the North Atlantic region. These extra peaks tend to contradict previous studies that interpreted the MIS 21 variability as consisting essentially of a linear response to cyclical changes in orbital parameters. Cooling events in the surface record during MIS 21 were associated with low benthic carbon isotope excursions, suggesting a coupling between surface temperature changes and the strength of the Atlantic meridional overturning circulation. Time series analysis performed on the whole interval indicates that benthic and planktonic oxygen isotopes have significant concentrations of spectral power centered on periods of 10.7 kyr and 6 kyr, which is in agreement with the second and forth harmonic of precession. The excellent correspondence between the foraminifera δ 18 O records and insolation variations at the Equator in March and September suggests that a mechanism related to low-latitude precession variations, advected to the high latitudes by tropical convective processes, might have generated such a response. This scenario accounts for the presence of oscillations at frequencies equal to precession harmonics at Site U1313, as well as the occurrence of higher amplitude oscillations between the MIS22/21 transition and most of MIS 21, times of enhanced insolation variability.
Mid Pleistocene climate instability in the subtropical northwestern Atlantic
Global and Planetary Change, 2006
We present Globigerinoides ruber, G. sacculifer and Neogloboquadrina dutertrei oxygen isotope records from northwestern subtropical Atlantic Site 1058 spanning the mid Pleistocene (∼ 600 to 400 ka). The high temporal resolution of these records (∼ 800 yr) allows us to compare millennial-scale climate signals during one of the most extreme glacial periods of the Pleistocene (Marine Isotope Stage (MIS) 12) to an earlier, less extreme glacial (MIS 14), as well as to two full interglacial intervals (MIS 13 and MIS 15). We observe excellent agreement in the timing and amplitude of variations between the surface-most dwelling species G. ruber and Northern Hemisphere insolation during the two interglacial periods. There is some expression of Northern Hemisphere insolation during glacial MIS 14; however, during the more extreme glacial MIS 12 Northern Hemisphere insolation patterns are not apparent in any of the planktonic foraminiferal δ 18 O records. Insolation remains relatively high, but δ 18 O values increase toward the characteristic δ 18 O maximum of MIS 12 in all three of the records. On the millennial-scale, all three species display their highest amplitude δ 18 O variations (with a period between 4-6 kyr) during glacial MIS 12. Suborbital-scale variability is also statistically significant during glacial MIS 14, but the amplitude is smaller. These results support hypotheses linking millennial-scale climate fluctuations to the extent of continental glaciation. We propose that the relatively high degree of sea surface instability during one of the most extreme glacial periods of the Pleistocene arises from the competing effects of strong atmospheric winds related to the presence of a large ice sheet to the north and persistently high incident solar radiation during this interval of time.
On the timing and mechanism of millennial-scale climate variability during the last glacial cycle
Climate Dynamics - CLIM DYNAM, 2002
The demonstration that natural climate variability during the last glacial cycle shifted rapidly between remarkable extremes has dramatically revised the understanding of climate change. To further advance our understanding, research continues into the timings, geographic distribution, and nature of the millennial-scale climate extremes, and into the mechanisms for intra- and inter-hemispheric transmission of variability through the climate/ocean system. Complementing the traditional definition of the timings of millennial-scale climate variability from ice-core delta18O records, we here further narrow down the temporal constraints by determining statistically significant anomalies in the major ion series of the GISP2 ice core. This exercise offers an objective definition of the timing of climatic anomalies in Northern Hemisphere palaeoclimate proxy records of the last 110,000 years that significantly improves the potential for inter-calibration of 'ice-core tuned' chronos...
SENSITIVITY OF SOUTH-EAST ATLANTIC PLANKTONIC FORAMINIFERA TO MID-PLEISTOCENE CLIMATE CHANGE
The last one million years are important in terms of climate development during the so-called Mid- Pleistocene Transition when amplification of the glacial– interglacial cycles occurred. This study describes abundance changes in fossil planktonic foraminifera in sediments from Core T89-40, retrieved from the Walvis Ridge in the southeast Atlantic, across this time period. Cycles between upwelling and subtropical planktonic foraminiferal assemblages are shown to mirror changes between glacial and interglacial periods, respectively. During interglacial marine isotopic stages (MIS) 9, 11 and 31, however, anomalously high abundances of the polar left-coiled Neogloboquadrina pachyderma occur, presumably linked to unusual seasonal upwelling waters. The planktonic foraminiferal abundance record shows 41-ky cyclic variations in the regional oceanography linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity). These orbitally induced oscillations in oceanographic change occurred throughout the entire record. The most conspicuous feature of the planktonic foraminiferal record is the near absence of left-coiled Globorotalia truncatulinoides between 960 and 610 ka (MIS 26-15). The abrupt disappearance of this species is synchronous with the onset of the Mid-Pleistocene Transition in MIS 26.
Paleoceanography, 2002
Considerable evidence now exists for high-frequency climate changes in the last ice age cycle (Dansgaard-Oeschger and Bond cycles). Though large-scale ice sheet flow has too long a time constant to play a significant role in these events, stochastically forced changes in the mass balance of the Pleistocene ice sheets may have resulted in significant variation in freshwater flux to the North Atlantic. In this paper we mimic the effects of ''natural climate variability'' with small (0.5W/m 2) stochastic changes in insolation and examine the response in terms of ice volume change in an ensemble of coupled energy balance/ice sheet model runs. The total change in ice mass is comparable to a third of the volume of the current Greenland ice sheet, with meltwater discharge potentially sufficient to trigger Dansgaard-Oeschger type events. In general, the Eurasian ice sheet is more sensitive to perturbations than the North American ice sheet. The distribution and occurrence of spectral peaks in the 1-9 kyr band is also comparable to the record of millennial oscillations over the last 500,000 years in a subpolar North Atlantic core. Our results suggest that considerable caution is necessary in interpreting the physical significance of sub-Milankovitch spectral peaks in paleo time series.
A 1.5-Million-Year Record of Orbital and Millennial Climate Variability in the North Atlantic
Climate during the last glacial period was marked by abrupt instability on millennial timescales that included large swings of temperature in and around Greenland (Daansgard-Oeschger events) and smaller, more gradual changes in Antarctica (AIM events). Less is known about the existence and nature of similar variability during older glacial periods, especially during the early Pleistocene when glacial cycles were dominantly occurring at 41 kyr intervals compared to the much longer and deeper glaciations of the more recent period. Here, we report a continuous millennially resolved record of stable isotopes of planktic and benthic foraminifera at IODP Site U1385 (the "Shackleton Site") from the southwestern Iberian margin for the last 1.5 million years, which includes the Middle Pleistocene Transition (MPT). Our results demonstrate that millennial climate variability (MCV) was a persistent feature of glacial climate, both before and after the MPT. Prior to 1.2 Ma in the early Pleistocene, the amplitude of MCV was modulated by the 41 kyr obliquity cycle and increased when axial tilt dropped below 23.5 • and benthic δ 18 O exceeded ∼ 3.8 ‰ (corrected to Uvigerina), indicating a threshold response to orbital forcing. Afterwards, MCV became focused mainly on the transitions into and out of glacial states (i.e. inceptions and terminations) and during times of intermediate ice volume. After 1.2 Ma, obliquity continued to play a role in modulating the amplitude of MCV, especially during times of glacial inceptions, which are always associated with declining obliq-uity. A non-linear role for obliquity is also indicated by the appearance of multiples (82, 123 kyr) and combination tones (28 kyr) of the 41 kyr cycle. Near the end of the MPT (∼ 0.65 Ma), obliquity modulation of MCV amplitude wanes as quasi-periodic 100 kyr and precession power increase, coinciding with the growth of oversized ice sheets on North America and the appearance of Heinrich layers in North Atlantic sediments. Whereas the planktic δ 18 O of Site U1385 shows a strong resemblance to Greenland temperature and atmospheric methane (i.e. Northern Hemisphere climate), millennial changes in benthic δ 18 O closely follow the temperature history of Antarctica for the past 800 kyr. The phasing of millennial planktic and benthic δ 18 O variation is similar to that observed for MIS 3 throughout much of the record, which has been suggested to mimic the signature of the bipolar seesaw-i.e. an interhemispheric asymmetry between the timing of cooling in Antarctica and warming in Greenland. The Iberian margin isotopic record suggests that bipolar asymmetry was a robust feature of interhemispheric glacial climate variations for at least the past 1.5 Ma despite changing glacial boundary conditions. A strong correlation exists between millennial increases in planktic δ 18 O (cooling) and decreases in benthic δ 13 C, indicating that millennial variations in North Atlantic surface temperature are mirrored by changes in deep-water circulation and remineralization of carbon in the abyssal ocean. We find strong evidence that climate variability on millennial and orbital scales is coupled Published by Copernicus Publications on behalf of the European Geosciences Union. 608 D. A. Hodell et al.: A 1.5-million-year record of orbital and millennial climate variability in the North Atlantic across different timescales and interacts in both directions, which may be important for linking internal climate dynamics and external astronomical forcing.