High- to low-latitude teleconnections during glacial terminations associated with ENSO-like variability

Long-term changes in ENSO-like dynamics during deglaciations are linked to southern high-latitude regions through atmospheric and oceanic teleconnection mechanisms

North Atlantic millennial-scale climate variability 910 to 790 ka and the role of the equatorial insolation forcing

The Mid-Pleistocene transition (MPT) was the time when quasi-periodic (not, vert, similar 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 δ18O 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

Contrasting intrainterstadial climatic evolution between high and middle North Atlantic latitudes: A close-up of Greenland Interstadials 8 and 12

Three highly resolved pollen and sea surface temperature records from the Iberian margin (36â "42°N) reveal the local evolution of vegetation and climate associated with the rapid climatic variability of marine isotope stage 3. The comparison of the climate at these midlatitudes with δD and d excess from Greenland ice cores shows that the northâ south climatic gradient underwent strong variations during the long Greenland Interstadials (GIs) 8 and 12. After the Northern Hemispheric rapid warming at the Greenland Stadial (GS)â GI transition, the trend during the first part of the GI is a Greenland cooling and an Iberian warming. This increase of the North Atlantic climatic gradient led to moisture transportation to Greenland from midlatitudes (lightest d excess) and to a drying episode in Iberia. The subsequent temperature decrease in Greenland and Iberia associated with the precipitation increase in the latter region occurred when the major source of Greenland precipitation shifted to lower latitudes (d excess increase)

Increased reservoir ages and poorly ventilated deep waters inferred in the glacial Eastern Equatorial Pacific

Consistent evidence for a poorly ventilated deep Pacific Ocean that could have released its radiocarbon-depleted carbon stock to the atmosphere during the last deglaciation has long been sought. Such evidence remains lacking, in part due to a paucity of surface reservoir age reconstructions required for accurate deep-ocean ventilation age estimates. Here we combine new radiocarbon data from the Eastern Equatorial Pacific (EEP) with chronostratigraphic calendar age constraints to estimate shallow sub-surface reservoir age variability, and thus provide estimates of deep-ocean ventilation ages. Both shallow- and deep-water ventilation ages drop across the last deglaciation, consistent with similar reconstructions from the South Pacific and Southern Ocean. The observed regional fingerprint linking the Southern Ocean and the EEP is consistent with a dominant southern source for EEP thermocline waters and suggests relatively invariant ocean interior transport pathways but significantly reduced air–sea gas exchange in the glacial southern high latitudes

Contrast sensitivity evaluation with filter contact lenses in patients with retinitis pigmentosa: a pilot study

Purpose: the aim of this pilot study was to test whether retinitis pigmentosa patients would benefit from filter contact lenses as an effective optical aid against glare and photophobia. Methods: fifteen subjects with retinitis pigmentosa were enrolled in this study. All of them were evaluated with filter soft contact lenses (MaxSight), filter glasses (CPF 527) and without filters (control). All patients were assessed for the three aid conditions by means of best corrected visual acuity (BCVA), contrast sensitivity (without glare and with central and peripheral glare)(CSV-1000) and a specific subjective questionnaire about quality of vision. Results: BCVA was slightly better with filters than without filter but the differences were not statistically significant. Contrast sensitivity without glare improved significantly with the contact lenses (p<0.05). The central glare had significant differences for the frequencies of 3 cpd and 18 cpd between the contact lens filter and the control group (p=0.021 and p=0.044, respectively). For the peripheral glare contrast sensitivity improved with contact lens versus control group for highest frequencies, 12 and 18 cpd (p<0.001 and p=0.045, respectively). According to the questionnaire the contact lens filter gave them more visual comfort than the glasses filter under the scenarios of indoors glare, outdoors activities and indoors comfort. Conclusion: the filter contact lenses seem to be a good option to improve the quality of vision of patients with retinitis pigmentosa

Increased reservoir ages and poorly ventilated deep waters inferred in the glacial Eastern Equatorial Pacific.

Consistent evidence for a poorly ventilated deep Pacific Ocean that could have released its radiocarbon-depleted carbon stock to the atmosphere during the last deglaciation has long been sought. Such evidence remains lacking, in part due to a paucity of surface reservoir age reconstructions required for accurate deep-ocean ventilation age estimates. Here we combine new radiocarbon data from the Eastern Equatorial Pacific (EEP) with chronostratigraphic calendar age constraints to estimate shallow sub-surface reservoir age variability, and thus provide estimates of deep-ocean ventilation ages. Both shallow- and deep-water ventilation ages drop across the last deglaciation, consistent with similar reconstructions from the South Pacific and Southern Ocean. The observed regional fingerprint linking the Southern Ocean and the EEP is consistent with a dominant southern source for EEP thermocline waters and suggests relatively invariant ocean interior transport pathways but significantly reduced air-sea gas exchange in the glacial southern high latitudes.We acknowledge funding by the Spanish Ministry of Economy and Competitiveness through grants CTM2009-08849 (ACDC Project) and CTM2012-32017 (MANIFEST Project). M. de la Fuente was funded by a FPI studentship (BES-2010-039700) from the Spanish Government, and L. Skinner acknowledges support from NERC grant NE/L006421/1.This is the final version. It first appeared at http://www.nature.com/ncomms/2015/150703/ncomms8420/full/ncomms8420.html

Nitrogen isotopic evidence for deglacial changes in nutrient supply in the eastern equatorial Pacific

The Eastern Equatorial Pacific (EEP) is a high nutrientâ "low chlorophyll region of the ocean. Downcore nitrogen isotope records from the EEP have been previously interpreted as a direct reflection of changes in nutrient consumption. However, the observed changes in sedimentary δ15N since the last glacial maximum have no coherent relationship with export productivity or an inferred variation in the iron-to-nitrate ratio of the surface waters. Rather, downcore N isotope records in the EEP strongly resemble changes in the extent of water column denitrification as recorded in nearby sedimentary δ15N records along the western margin of the Americas. This similarity is attributed to the overprinting of the N isotopic composition of nitrate in the EEP through the advection of nitrate westward from the margins in the subsurface. A local nitrogen isotope record of changes in the degree of nutrient consumption is extracted from the bulk sedimentary record by subtracting two different sedimentary δ15N records of denitrification changes from two new EEP δ15N records (TR163-22 and ODP Site 1240). The denitrification records used are from 1) the Central American margin (ODP Site 1242) and 2) the South American margin (GeoB7139-2). The degree of consumption in the surface waters declines rapidly from elevated values during the last glacial maximum to a pair of minima around 15 and 11â "13 ka, and finally it increases into the Holocene. The derived EEP nitrogen isotope record indicates that the regional peak in export productivity occurred when the supply of nutrients exceeded the apparently high demand. The influx of nutrients during the deglaciation is attributed to the resumption of intense overturning in the Southern Ocean and the release of sequestered CO2 and nutrient-rich, O2 poor waters from the deep ocean. This has important implications for understanding the glacial-interglacial scale variation in intermediate water suboxia and water column denitrification

Identification and removal of Mn-Mg-rich contaminant phases in foraminiferal tests: Implications for Mg/Ca past temperature reconstructions

The geochemical composition of foraminifera shells from an Ocean Drilling Program site in the Panama Basin has been analyzed by several analytical techniques (LA-ICP-MS, ICP-MS, XRD, SEM, EDX) in order to identify and evaluate the occurrence of contaminant phases which may bias paleoenvironmental reconstructions. LA-ICP-MS results on uncleaned tests indicate the presence of Mn-Mg-rich contaminant phases at the inner surfaces of the foraminiferal shells (which have Mn/Ca ratios up to 400 mmol mol-1 and Mg/Ca ratios up to 50 mmol mol-1). We have rigorously assessed the ability of different cleaning protocols to remove these contaminant phases and have obtained satisfactory results only when a reductive step is included. The analysis of cleaning residuals collected after each of the different cleaning steps applied reveals that high Mn values are associated with at least two different contaminant phases, of which only one is linked to high Mg values. XRD analysis further reveals that the Mn-Mg-rich phase is the Ca-Mn-Mg carbonate kutnahorite (Ca(Mn, Mg)(CO3)2). Our results demonstrate that the presence of kutnahorite-like minerals can bias Mg/Ca ratios toward higher values (by 7-36%) and lead to significant overestimation of past seawater temperatures (by 0.9 up to 6.2°C, in the case of these Panama Basin samples)