Glacials and Interglacials

Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550 kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation. Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers' results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.

In the southern Indian Ocean, the position of the subtropical front – the boundary between colder, fresher waters to the south and warmer, saltier waters to the north – has a strong influence on the upper ocean hydrodynamics and biogeochemistry. Here we analyse a sedimentary record from the Agulhas Plateau, located close to the modern position of the subtropical front and use alkenones and coccolith assemblages to reconstruct oceanographic conditions over the past 300,000 years. We identify a strong glacial-interglacial variability in sea surface temperature and productivity associated with subtropical front migration over the Agulhas Plateau, as well as shorter-term high frequency variability aligned with variations in high latitude insolation. Alkenone and coccolith abundances, in combination with diatom and organic carbon records indicate high glacial export productivity. We conclude that the biological pump was more efficient and strengthened during glacial periods, which could ...

A geoarchaeological study of sediments in the Azraq Oasis, in the Eastern Desert of Jordan, provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local Middle Paleolithic and Upper Paleolithic occupations. The study shows that local geomorphic and hydrological environments fluctuated between marsh, lake and playa (dry lake bed with eolian activity and/or carbonate accumulation). In some instances, local wet conditions correlate with those registered in other regional paleoclimatic records, as is the case of the period comprising MIS 5a and probably early MIS 4. In other cases, however, local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions. This suggests that the Azraq oases may have acted as desert refugia at times of regional adverse climatic conditions. The fact that Azraq represents a potential desert refugia has important consequences for understanding major issues in the Middle Paleolithic of Southwest Asia, namely (1) the arrival, survival, and extinction of populations of both Neanderthals and early modern humans. The location of Azraq at a crossroads between the Levant, the Arabian Peninsula and other regions of the Middle East, is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the Middle Paleolithic.

A geoarchaeological study of sediments in the Azraq Oasis, in the Eastern Desert of Jordan, provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local Middle Paleolithic and Upper Paleolithic occupations. The study shows that local geomorphic and hydrological environments fluctuated between marsh, lake and playa (dry lake bed with eolian activity and/or carbonate accumulation). In some instances, local wet conditions correlate with those registered in other regional paleoclimatic records, as is the case of the period comprising MIS 5a and probably early MIS 4. In other cases, however, local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions. This suggests that the Azraq oases may have acted as desert refugia at times of regional adverse climatic conditions. The fact that Azraq represents a potential desert refugia has important consequences for understanding major issues in the Middle Paleolithic of Southwest Asia, namely (1) the arrival, survival, and extinction of populations of both Neanderthals and early modern humans. The location of Azraq at a crossroads between the Levant, the Arabian Peninsula and other regions of the Middle East, is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the Middle Paleolithic.

Stalagmite Orum-1 from a cave near Orumana in northwestern Namibia provides a multiproxy record of regional drying with increasing global-scale warmth over the last 47 kyr, in a region with few long well-dated location-specific paleoclimate records. Data from Stalagmite Orum-1 include carbon and oxygen stable isotope ratios, proportions of aragonite and calcite, pronouncedly differing petrographic fabrics, positions of layer-bounding surfaces, variation in layer-specific width, and changes in layer thickness, all of which combine to support change from wetter to drier conditions. Combined with fourteen U-Th ages, they suggest that climate was wetter in northwestern Namibia during globally cold MIS 3 than it is today, and with more grass than is present today. The climate at Orumana became drier during the deglacial transition after the Last Glacial Maximum, but carbon isotope data indicate that C 4 grasses persisted. In the Holocene, even greater aridity led to a reduction in grass cover and to the present C 3-dominated vegetation. Hiatuses in Stalagmite Orum-1 suggest even drier conditions during the Bølling-Allerød and during the early Holocene thermal maximum. Wetter conditions at Orumana during glacial times may have resulted from movement of the Intertropical Convergence Zone southward, in a shift that was significant west of longitude 13°E but perhaps less significant east of that line. It may have been accompanied by a lesser southward shift of the Angola-Benguela Front at sea and/or the Inter-Ocean Convergence Zone on land, leading to increased rainfall in northern Namibia (but perhaps not farther south). Extrapolation from the present to warmer conditions in the next century would suggest that further drying in northern Namibia and southern Angola may occur.

Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550 kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation. Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers' results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.

Globally, inland waters emit over 2 Pg of carbon per year as carbon dioxide, of which the majority originates from streams and rivers. Despite the global significance of fluvial carbon dioxide emissions, little is known about their diel dynamics. Here we present a large-scale assessment of day- and night-time carbon dioxide fluxes at the water-air interface across 34 European streams. We directly measured fluxes four times between October 2016 and July 2017 using drifting chambers. Median fluxes are 1.4 and 2.1 mmol m−2 h−1 at midday and midnight, respectively, with night fluxes exceeding those during the day by 39%. We attribute diel carbon dioxide flux variability mainly to changes in the water partial pressure of carbon dioxide. However, no consistent drivers could be identified across sites. Our findings highlight widespread day-night changes in fluvial carbon dioxide fluxes and suggest that the time of day greatly influences measured carbon dioxide fluxes across European streams.

The Southern Hemisphere westerly winds sustain the Southern Ocean’s role as one of Earth’s main carbon sinks, and have helped sequester nearly half the anthropogenic CO2 stored in the ocean. Observations show shifts in the vigor of this climate regulator, but models disagree how future change impacts carbon storage due to scarce baseline data. Here, we use the hydrogen isotope ratios of sedimentary lipids to resolve Holocene changes in Southern Hemisphere westerly wind strength. Our reconstruction reveals stable values until ~2150 years ago when aquatic compounds became more 2H-enriched. We attribute this isotope excursion to wind-driven lake water evaporation, and regional paleoclimate evidence shows it marks a trend towards a negative Southern Annular Mode – the Southern Ocean’s main mode of atmospheric variability. Because this shift is unmatched in the past 7000 years, our findings suggest that previously published millennium-long Southern Annular Mode indices used to benchmark ...

In the southern Indian Ocean, the position of the subtropical front – the boundary between colder, fresher waters to the south and warmer, saltier waters to the north – has a strong influence on the upper ocean hydrodynamics and biogeochemistry. Here we analyse a sedimentary record from the Agulhas Plateau, located close to the modern position of the subtropical front and use alkenones and coccolith assemblages to reconstruct oceanographic conditions over the past 300,000 years. We identify a strong glacial-interglacial variability in sea surface temperature and productivity associated with subtropical front migration over the Agulhas Plateau, as well as shorter-term high frequency variability aligned with variations in high latitude insolation. Alkenone and coccolith abundances, in combination with diatom and organic carbon records indicate high glacial export productivity. We conclude that the biological pump was more efficient and strengthened during glacial periods, which could partly account for the reported reduction in atmospheric carbon dioxide concentrations.

The Ma'in Site is a complex of Paleolithic sites located on the western rim of the Madaba Plateau, above the escarpment facing the Dead Sea Rift. The site was a lithic acquisition and initial processing location used primarily by both Middle Paleolithic peoples and unidentified groups in the early Holocene. It also includes some late Lower Paleolithic Acheulo-Yabrudian material. Numeric dates place most of the MP at the site in Marine Isotopic Stages 5e-a, which is consistent with a middle MP attribution, as is the predominance of Levallois flake cores in the archaeological collections. The geoarchaeological study of the site produced information concerning the geological, pedological and paleoenvironmental context of the lithic material supported by OSL and U-series dating. The sequences of sediments and soils provide the means for reconstructing the geomorphological history of the site. Based on soil development, the wet periods are

The Ma'in Site is a complex of Paleolithic sites located on the western rim of the Madaba Plateau, above the escarpment facing the Dead Sea Rift. The site was a lithic acquisition and initial processing location used primarily by both Middle Paleolithic peoples and unidentified groups in the early Holocene. It also includes some late Lower Paleolithic Acheulo-Yabrudian material. Numeric dates place most of the MP at the site in Marine Isotopic Stages 5e-a, which is consistent with a middle MP attribution, as is the predominance of Levallois flake cores in the archaeological collections. The geoarchaeological study of the site produced information concerning the geological, pedological and paleoenvironmental context of the lithic material supported by OSL and U-series dating. The sequences of sediments and soils provide the means for reconstructing the geomorphological history of the site. Based on soil development, the wet periods are

The mid-Holocene climate of Northwest Arabia is characterised by a significant increase in aridity which gave rise to changes in water management strategies including sophisticated techniques at later stages. The Rasif site, situated in Northwest Saudi Arabia, reveals a Late Neolithic society with multi-roomed domestic structures (1st phase, 6th millennium BCE, before the current era). At Rasif site the sediments of an endorheic basin (qa) show a minimum in salinity during this 1st phase. The 2nd phase is characterised by a pastoral ‘Chalcolithic’ watering and ‘Chalcolithic’ burial location of the 5th millennium BCE with wells, complex trough systems, and initial, probably coexistent grave structures. During this 2nd phase the qa deposits show already a slight increase in salinity. We have evidence for a sub-surface water-rich sand layer within the qa that was exploited by shallow wells. During the subsequent 3rd phase the number of pastoral ‘Chalcolithic’ D-shaped grave structures within the qa increased, probably co-existing with deepened wells and complex trough systems. At that time the qa is covered by an almost impermeable saline clay layer. The 4th phase is characterised by a culturally yet to identify pastoral post-‘Chalcolithic’ watering location with single small troughs. The final 5th phase represents a culturally unidentified pastoral post-’Chalcolithic’ to sub-recent water harvesting location with complex dam systems, which were probably modified numerous times. The dam systems allowed to flooding the qas for several months, providing (sub-) surface water in the nowadays Northwest Arabian desert.

(Seventy U-Th ages from six stalagmites from the Cordillera Cantábrica in northwestern Spain indicate deposition during interglacial, but not glacial, stages over the last 550 kyr. Stable isotope data and petrographic observations suggest that, within each interglacial, conditions typically progressed from drier to wetter. Consideration of the most precise U-Th ages suggests that stalagmite deposition occurred in times more predictable from European pollen records than from the global marine isotope record. For example, during the last interglacial, ages suggest deposition in an interval better characterized as the Eemian, as opposed to MIS 5e, and during the St. Germain I or MIS 5c interval. The same holds for MIS 7, where ages suggest deposition during MIS 7a and MIS 7c but not MIS 7e. These age ranges for interglacials, consistently later than those suggested by the benthic marine record, are compatible with warm conditions maintained by thermohaline circulation that simultaneously supplied the moisture for growing ice sheets of the subsequent glaciation.
Trends both within and across these six stalagmites suggest that cooler temperatures were associated with wetter conditions, both during interglacials and in conditions intermediate between interglacials and glacials in northern Spain. In contrast, other researchers’ results from a stalagmite from the Last Glacial Maximum and subsequent deglaciation suggest colder temperatures were associated with drier conditions. The two trends combine to suggest wettest conditions in times intermediate between interglacials and glacials, compatible with a model in which modern climatic belts from dry Arctic to wet European to dry marginal Saharan have moved over northern Spain in the cycle from glacial to interglacial times. Extrapolation to a warmer future would suggest drier conditions in the northern Iberian Peninsula than those of today.)

A geoarchaeological study of sediments in the Azraq Oasis, in the Eastern Desert of Jordan, provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local Middle Paleolithic and Upper Paleolithic occupations. The study shows that local geomorphic and hydrological environments fluctuated between marsh, lake and playa (dry lake bed with eolian activity and/or carbonate accumulation). In some instances, local wet conditions correlate with those registered in other regional paleoclimatic records, as is the case of the period comprising MIS 5a and probably early MIS 4. In other cases, however, local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions. This suggests that the Azraq oases may have acted as desert refugia at times of regional adverse climatic conditions. The fact that Azraq represents a potential desert refugia has important consequences for understanding major issues in the Middle Paleolithic of Southwest Asia, namely (1) the arrival, survival, and extinction of populations of both Neanderthals and early modern humans. The location of Azraq at a crossroads between the Levant, the Arabian Peninsula and other regions of the Middle East, is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the Middle Paleolithic.

A geoarchaeological study of sediments in the Azraq Oasis, in the Eastern Desert of Jordan, provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local Middle Paleolithic and Upper Paleolithic occupations. The study shows that local geomorphic and hydrological environments fluctuated between marsh, lake and playa (dry lake bed with eolian activity and/or carbonate accumulation). In some instances, local wet conditions correlate with those registered in other regional paleoclimatic records, as is the case of the period comprising MIS 5a and probably early MIS 4. In other cases, however, local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions. This suggests that the Azraq oases may have acted as desert refugia at times of regional adverse climatic conditions. The fact that Azraq represents a potential desert refugia has important consequences for understanding major issues in the Middle Paleolithic of Southwest Asia, namely (1) the arrival, survival, and extinction of populations of both Neanderthals and early modern humans. The location of Azraq at a crossroads between the Levant, the Arabian Peninsula and other regions of the Middle East, is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the Middle Paleolithic.

A geoarchaeological study of sediments in the Azraq Oasis, in the Eastern Desert of Jordan, provides information on the fluctuations of the geomorphic and hydrologic systems in this region in relation to the local Middle Paleolithic and Upper Paleolithic occupations. The study shows that local geomorphic and hydrological environments fluctuated between marsh, lake and playa (dry lake bed with eolian activity and/or carbonate accumulation). In some instances, local wet conditions correlate with those registered in other regional paleoclimatic records, as is the case of the period comprising MIS 5a and probably early MIS 4. In other cases, however, local wet conditions represented by marsh deposits with hominin occupations are asynchronous with regional wet conditions. This suggests that the Azraq oases may have acted as desert refugia at times of regional adverse climatic conditions. The fact that Azraq represents a potential desert refugia has important consequences for understanding major issues in the Middle Paleolithic of Southwest Asia, namely (1) the arrival, survival, and extinction of populations of both Neanderthals and early modern humans. The location of Azraq at a crossroads between the Levant, the Arabian Peninsula and other regions of the Middle East, is also an important geographic aspect of desert refugia during the critical period of hominin dynamics in the Middle Paleolithic.