Centennial-scale vegetation and North Atlantic Oscillation changes during the Late Holocene in the southern Iberia

High-reso CE to lution pollen analysis, charcoal, non-pollen palynomorphs and magnetic susceptibility have been analyzed in the sediment record of a peat bog in Sierra Nevada in southern Iberia. The study of these proxies provided the reconstruction of vegetation, climate, fire and human activity of the last ∼4500 cal yr BP. A progressive trend towards aridification during the late Holocene is observed in this record. This trend is interrupted by millennial- and centennial-scale variability of relatively more humid and arid periods. Arid conditions are recorded between ∼4000 and 3100 cal yr BP, being characterized by a decline in arboreal pollen and with a spike in magnetic susceptibility. This is followed by a relatively humid period from ∼3100 to 1600 cal yr BP, coinciding partially with the Iberian-Roman Humid Period, and is indicated by the increase of Pinus and the decrease in xerophytic taxa. The last 1500 cal yr BP are characterized by several centennial-scale climatic oscillations. Generally arid conditions from ∼450 to 1300 CE, depicted by a decrease in Pinus and an increase in Artemisia, comprise the Dark Ages and the Medieval Climate Anomaly. Since ∼ 1300 to 1850 CE pronounced oscillations occur between relatively humid and arid conditions. Four periods depicted by relatively higher Pinus coinciding with the beginning and end of the Little Ice Age are interrupted by three arid events characterized by an increase in Artemisia. These alternating arid and humid shifts could be explained by centennial-scale changes in the North Atlantic Oscillation and solar activity

Evidence of early bottom water current flow after the Messinian Salinity Crisis in the Gulf of Cadiz

Highlights • Stratigraphic framework over the Miocene-Pliocene boundary at IODP Site U1387. • Abrupt sedimentary changes over the Miocene-Pliocene boundary. • Clear hints for onset of Mediterranean Outflow after the Messinian Salinity Crisis. • Evidence of bottom water currents in contouritic sedimentation and elevated Zr/Al. • Quiet, hemipelagic sediment deposition during the Messinian in the Gulf of Cadiz. Abstract Integrated Ocean Drilling Program (IODP) Expedition 339 cored multiple sites in the Gulf of Cadiz in order to study contourite deposition resulting from Mediterranean Outflow water (MOW). One hole, U1387C, was cored to a depth of 865.6 meters below seafloor (mbsf) with the goal of recovering the Latest Miocene to Pliocene transition in order to evaluate the history of MOW immediately after the end of the Messinian Salinity Crisis. To understand this history, an accurate age model for the succession is needed, but is challenging to construct, because the Miocene-Pliocene boundary is not marked by a clear biostratigraphic event in the Atlantic and coring gaps occur within the recovered stratigraphic record. These limitations are overcome by combining a variety of chronostratigraphic datasets to construct an age-model that fits the currently available age indicators and demonstrates that coring in Hole U1387C did indeed recover the Miocene-Pliocene boundary at around 826 mbsf. This boundary is associated with a distinct and abrupt change in depositional environment. During the latest Messinian, hemipelagic sediments exhibiting precession-induced climate variability were deposited. These are overlain by Pliocene sediments deposited at a much higher sedimentation rate, with much higher and more variable XRF-scanning Zr/Al ratios than the underlying sediment, and that show evidence of winnowing, particle sorting and increasing grain size, which we interpret to be related to the increasing flow of MOW. Pliocene sedimentary cyclicity is clearly visible in both the benthic δ18O record and the Zr/Al data and is probably also precessionally controlled. Two contouritic bigradational sandy-beds are revealed above the third sedimentary cycle of the Pliocene. On the basis of these results, we conclude that sedimentation associated with weak Mediterranean-Atlantic exchange, began in the Gulf of Cadiz virtually at or shortly after the Miocene-Pliocene boundary

Impact of the Mediterranean-Atlantic connectivity and the late Miocene carbon shift on deep-sea communities in the Western Alboran Basin

Integration of foraminiferal and geochemical data (stable isotope and elemental composition) from West Alboran Basin (WAB) ODP Site 976 allowed evaluation of the effects of the initial Mediterranean – Atlantic restriction event preceding the Messinian Salinity Crisis (MSC) in a context of late Miocene cooling and diminishing water – mass exchange close to Gibraltar Strait. At 7.17 Ma a prominent shift in benthic foraminifer abundances from dominantly oxic taxa to species tolerating oxygen deficiency, paired with a drop in δ13C values, suggest that the restriction of the Mediterranean-Atlantic gateways profoundly affected the WAB deep waters. From 7.17 Ma onward, deep-water stagnation increased the bottom water residence time and led to oxygen depletion. Similar changes, already identified in other Mediterranean basins imply that the first signs of Mediterranean-Atlantic restriction significantly predated the onset of the MSC also in the WAB, an area sometimes considered more under the influence of the Atlantic. Simultaneously, a marked amplitude increase of several element-log ratios reveals a clear cyclical pattern related with precession. Together with new δ18O data, the identification of cyclical patterns allowed improving the age model of Site 976 and consequently enabled an accurate correlation with other Mediterranean, mostly land-based sections. Comparing the records, we were able to correlate the event at a basinal scale and to refine thermohaline circulation models of the Mediterranean after 7.17 Ma. Because this Mediterranean-scale change was contemporaneous with the global Late Miocene Carbon Isotope Shift (LMCIS) it was important to discern between global and local effects. Given the synchronicity of the global and local Mediterranean change in the δ13C record, a global effect certainly affected the Mediterranean Basin. However, opposite phase relations of the global and local δ13C signals with orbital parameters, paired with a higher magnitude change identified in our WAB isotope record suggests that the local imprint overruled the global one

Radiogenic isotopes for deciphering terrigenous input provenance in the western Mediterranean

Radiogenic isotopic signatures in marine sediments can be used to trace terrigenous source areas and transport mechanisms, which are in turn related to climate variability. To date, most of the published studies using this approach have been focused on eastern Mediterranean sediments. In contrast, we study here the terrigenous input provenance in the westernmost Mediterranean (Alboran Sea basin) by using radiogenic isotope proxies and Nd model ages in a marine record spanning the last 20 ka. Nd, Sr and Pb isotopes, obtained from carbonate-free samples from the < 37μm size fraction, were used to characterize terrigenous variations, including eolian input. Substantial shifts in Pb isotopic signatures throughout the studied time interval reveal a change from North African dominated sources during the glacial period to European dominated sources during the Holocene. Nd and Sr shifts likewise indicate two main short-term changes in sediment provenance, during the last Heinrich event and the early-middle Holocene transition (ca. 8.9 ka cal. BP). Nd model ages over 1.45 Ga also support a contribution of an older component in the terrigenous source, likely Archaean material from the present Senegal region, during both periods. Conversely, terrigenous material mainly shows a dominant provenance from present-day Morocco, Mali, Mauritania, Niger, and Algeria, mixed with material from southern Iberia and southern France. Source variations in the westernmost Mediterranean were mainly driven by fluctuations in wind intensity and fluvial discharges. These fluctuations seem to have been modulated by the African monsoon system further conditioned by the ITZC migrations and the position of the North Atlantic anticyclone system

Paleocirculation and paleoclimate conditions in the western Mediterranean basins over the last deglaciation: New insights from sediment composition variations

We present a high-resolution analysis of seven marine sediment records from the western Mediterranean in a transect from the Algero-Balearic basin to the Alboran Sea, spanning the last 20 ka, to decipher the paleoenvironmental and paleoceanographic evolution of the western Mediterranean Sea. To do so, diverse elemental ratios have been used for reconstructing sediment input variations and paleo-oxygen conditions. In particular, the Ti/Ca ratio has been used to reconstruct variations in the terrigenous and carbonate fractions. However, the specific sedimentary processes controlling this ratio are still poorly understood thus, we also provide new insights for appropriate interpretations in the studied zone. Our results suggest that the Ti/Ca ratio at the suborbital scale is mostly controlled by bottom current intensity, and less influenced by marine productivity, sea level variations and fluvial and eolian inputs. Comparison of diverse records within the western Mediterranean reveals that the Ti/Ca ratio depicted a similar trend in both regions, except during the Heinrich Stadial 1 (HS1) and the Middle Holocene. The HS1 is recorded as a single-phase event in the Algero-Balearic basin, whereas three phases are recognized in the Alboran Sea basin, with a relative minimum in the Ti/Ca ratio. Conversely, during the Middle Holocene, an increase in the Ti/Ca ratio is recorded in the Alboran Sea but not in the Algero-Balearic basin, which could be related to the establishment of the Alboran gyres. Redox sensitive proxies, in particular the Mo/Al, U/Al and Mn/Al ratios, point to different phases within the Organic Rich Layer 1 (ORL1): the ORL1a (15- 11.7 ka cal BP), characterized by more reducing conditions in the Alboran Sea sediments, and the ORL1b 11.7- ~9 ka cal BP) characterized by suboxic-ferruginous conditions. The sea level transgression, the enhanced fluvial input and the shelf flooding played a key role during the ORL1 onset and demise, ncreasing the sedimentation rate in the basin and preventing the organic matter oxidation. During the last 2 ka cal BP, an unprecedented common response is recognized in all the studied regions, showing an overall increase in the Ti/Ca ratio, which may be related to intensified human activity in the Mediterranean area, promoting a greater terrigenous input.Postprin

Impact of the Mediterranean-Atlantic connectivity and the late Miocene carbon shift on deep-sea communities in the Western Alboran Basin

Integration of foraminiferal and geochemical data (stable isotope and elemental composition) from West Alboran Basin (WAB) ODP Site 976 allowed evaluation of the effects of the initial Mediterranean – Atlantic restriction event preceding the Messinian Salinity Crisis (MSC) in a context of late Miocene cooling and diminishing water – mass exchange close to Gibraltar Strait. At 7.17 Ma a prominent shift in benthic foraminifer abundances from dominantly oxic taxa to species tolerating oxygen deficiency, paired with a drop in δ13C values, suggest that the restriction of the Mediterranean-Atlantic gateways profoundly affected the WAB deep waters. From 7.17 Ma onward, deep-water stagnation increased the bottom water residence time and led to oxygen depletion. Similar changes, already identified in other Mediterranean basins imply that the first signs of Mediterranean-Atlantic restriction significantly predated the onset of the MSC also in the WAB, an area sometimes considered more under the influence of the Atlantic. Simultaneously, a marked amplitude increase of several element-log ratios reveals a clear cyclical pattern related with precession. Together with new δ18O data, the identification of cyclical patterns allowed improving the age model of Site 976 and consequently enabled an accurate correlation with other Mediterranean, mostly land-based sections. Comparing the records, we were able to correlate the event at a basinal scale and to refine thermohaline circulation models of the Mediterranean after 7.17 Ma. Because this Mediterranean-scale change was contemporaneous with the global Late Miocene Carbon Isotope Shift (LMCIS) it was important to discern between global and local effects. Given the synchronicity of the global and local Mediterranean change in the δ13C record, a global effect certainly affected the Mediterranean Basin. However, opposite phase relations of the global and local δ13C signals with orbital parameters, paired with a higher magnitude change identified in our WAB isotope record suggests that the local imprint overruled the global one

Paleocirculation and paleoclimate conditions in the western Mediterranean basins over the last deglaciation: New insights from sediment composition variations

We present a high-resolution analysis of seven marine sediment records from the western Mediterranean in a transect from the Algero-Balearic basin to the Alboran Sea, spanning the last 20 ka, to decipher the paleoenvironmental and paleoceanographic evolution of the western Mediterranean Sea. To do so, diverse elemental ratios have been used for reconstructing sediment input variations and paleo-oxygen conditions. In particular, the Ti/Ca ratio has been used to reconstruct variations in the terrigenous and carbonate fractions. However, the specific sedimentary processes controlling this ratio are still poorly understood thus, we also provide new insights for appropriate interpretations in the studied zone. Our results suggest that the Ti/Ca ratio at the suborbital scale is mostly controlled by bottom current intensity, and less influenced by marine productivity, sea level variations and fluvial and eolian inputs. Comparison of diverse records within the western Mediterranean reveals that the Ti/Ca ratio depicted a similar trend in both regions, except during the Heinrich Stadial 1 (HS1) and the Middle Holocene. The HS1 is recorded as a single-phase event in the Algero-Balearic basin, whereas three phases are recognized in the Alboran Sea basin, with a relative minimum in the Ti/Ca ratio. Conversely, during the Middle Holocene, an increase in the Ti/Ca ratio is recorded in the Alboran Sea but not in the Algero-Balearic basin, which could be related to the establishment of the Alboran gyres. Redox sensitive proxies, in particular the Mo/Al, U/Al and Mn/Al ratios, point to different phases within the Organic Rich Layer 1 (ORL1): the ORL1a (15- 11.7 ka cal BP), characterized by more reducing conditions in the Alboran Sea sediments, and the ORL1b 11.7- ~9 ka cal BP) characterized by suboxic-ferruginous conditions. The sea level transgression, the enhanced fluvial input and the shelf flooding played a key role during the ORL1 onset and demise, ncreasing the sedimentation rate in the basin and preventing the organic matter oxidation. During the last 2 ka cal BP, an unprecedented common response is recognized in all the studied regions, showing an overall increase in the Ti/Ca ratio, which may be related to intensified human activity in the Mediterranean area, promoting a greater terrigenous input.S