Monsoon-driven Saharan dust variability over the past 240,000 years.

Reconstructions of past Saharan dust deposition in marine sediments provide foundational records of North African climate over time scales of 103 to 106 years. Previous dust records show primarily glacial-interglacial variability in the Pleistocene, in contrast to other monsoon records showing strong precessional variability. Here, we present the first Saharan dust record spanning multiple glacial cycles obtained using 230Th normalization, an improved method of calculating fluxes. Contrary to previous data, our record from the West African margin demonstrates high correlation with summer insolation and limited glacial-interglacial changes, indicating coherent variability in the African monsoon belt throughout the late Pleistocene. Our results demonstrate that low-latitude Saharan dust emissions do not vary synchronously with high- and mid-latitude dust emissions, and they call into question the use of existing Plio-Pleistocene dust records to investigate links between climate and hominid evolution.

Repeated storage of respired carbon in the equatorial Pacific Ocean over the last three glacial cycles.

As the largest reservoir of carbon exchanging with the atmosphere on glacial-interglacial timescales, the deep ocean has been implicated as the likely location of carbon sequestration during Pleistocene glaciations. Despite strong theoretical underpinning for this expectation, radiocarbon data on watermass ventilation ages conflict, and proxy interpretations disagree about the depth, origin and even existence of the respired carbon pool. Because any change in the storage of respiratory carbon is accompanied by corresponding changes in dissolved oxygen concentrations, proxy data reflecting oxygenation are valuable in addressing these apparent inconsistencies. Here, we present a record of redox-sensitive uranium from the central equatorial Pacific Ocean to identify intervals associated with respiratory carbon storage over the past 350 kyr, providing evidence for repeated carbon storage over the last three glacial cycles. We also synthesise our data with previous work and propose an internally consistent picture of glacial carbon storage and equatorial Pacific Ocean watermass structure.

No iron fertilization in the equatorial Pacific Ocean during the last ice age.

The equatorial Pacific Ocean is one of the major high-nutrient, low-chlorophyll regions in the global ocean. In such regions, the consumption of the available macro-nutrients such as nitrate and phosphate is thought to be limited in part by the low abundance of the critical micro-nutrient iron. Greater atmospheric dust deposition could have fertilized the equatorial Pacific with iron during the last ice age--the Last Glacial Period (LGP)--but the effect of increased ice-age dust fluxes on primary productivity in the equatorial Pacific remains uncertain. Here we present meridional transects of dust (derived from the (232)Th proxy), phytoplankton productivity (using opal, (231)Pa/(230)Th and excess Ba), and the degree of nitrate consumption (using foraminifera-bound δ(15)N) from six cores in the central equatorial Pacific for the Holocene (0-10,000 years ago) and the LGP (17,000-27,000 years ago). We find that, although dust deposition in the central equatorial Pacific was two to three times greater in the LGP than in the Holocene, productivity was the same or lower, and the degree of nitrate consumption was the same. These biogeochemical findings suggest that the relatively greater ice-age dust fluxes were not large enough to provide substantial iron fertilization to the central equatorial Pacific. This may have been because the absolute rate of dust deposition in the LGP (although greater than the Holocene rate) was very low. The lower productivity coupled with unchanged nitrate consumption suggests that the subsurface major nutrient concentrations were lower in the central equatorial Pacific during the LGP. As these nutrients are today dominantly sourced from the Subantarctic Zone of the Southern Ocean, we propose that the central equatorial Pacific data are consistent with more nutrient consumption in the Subantarctic Zone, possibly owing to iron fertilization as a result of higher absolute dust fluxes in this region. Thus, ice-age iron fertilization in the Subantarctic Zone would have ultimately worked to lower, not raise, equatorial Pacific productivity.

Large deglacial shifts of the Pacific Intertropical Convergence Zone.

The position of the Intertropical Convergence Zone (ITCZ) is sensitive to changes in the balance of heat between the hemispheres which has fundamental implications for tropical hydrology and atmospheric circulation. Although the ITCZ is thought to experience the largest shifts in position during deglacial stadial events, the magnitude of shifts has proven difficult to reconstruct, in part because of a paucity of high-resolution records, particularly those including spatial components. Here we track the position of the ITCZ from 150 to 110 ka at three sites in the central equatorial Pacific at sub-millennial time resolution. Our results provide evidence of large, abrupt changes in tropical climate during the penultimate deglaciation, coincident with North Atlantic Heinrich Stadial 11 (∼136-129 ka). We identify this event both as a Northern Hemisphere increase in aeolian dust and as a shift in the mean position of the ITCZ a minimum of 4° southwards at 160° W.

Increased dust deposition in the Pacific Southern Ocean during glacial periods.

Dust deposition in the Southern Ocean constitutes a critical modulator of past global climate variability, but how it has varied temporally and geographically is underdetermined. Here, we present data sets of glacial-interglacial dust-supply cycles from the largest Southern Ocean sector, the polar South Pacific, indicating three times higher dust deposition during glacial periods than during interglacials for the past million years. Although the most likely dust source for the South Pacific is Australia and New Zealand, the glacial-interglacial pattern and timing of lithogenic sediment deposition is similar to dust records from Antarctica and the South Atlantic dominated by Patagonian sources. These similarities imply large-scale common climate forcings, such as latitudinal shifts of the southern westerlies and regionally enhanced glaciogenic dust mobilization in New Zealand and Patagonia.

[Peculiarities of the innervation of some muscles in the oto-rhino-laryngological region]. / Particularités de l'innervation de certains muscles dans le domaine oto-rhino-laryngologique.

This study shows different aspects of the innervation of some striated muscles. It appears that neuromuscular spindles are not present in all skeletal muscles. Some muscles of the oto-rhino-laryngological region lack spindles whilst their direct antagonists possess them. Amongst the muscles of the external and middle ear, the soft palate and the larynx having opposite actions, there is in each case one muscle which does not have any spindles. These muscles then have only motor innervation. The muscles which have neuro-muscular spindles are innervated by nerves composed of extra- and intrafusal motor fibres and proprioceptive fibres. The neuro-muscular spindles play a servo-braking role in the muscle where they occur. The oppose then a certain passive elongation of the muscle. At the same time and in this manner, they contribute in controlling and restraining the action of the muscles or of their opponents. This role is particularly important for the various muscles of the oto-rhino-laryngological region and is all the more important since the amplitude of the movements which they cause is very weak. The presence of these spindles increases also the sensitivity and the delicacy of the desired movement, for the behaviour of these muscles is very special. (See formula in text).

[Characteristics of the innervation of various muscles in the ear, nose and throat area]. / Particularités de l'innervation de certains muscles dans le domaine oto-rhino-laryngologique.

This study shows different aspects of the innervation of some striated muscles. It appears that neuromuscular spindles are not present in all skeletal muscles. Some muscles of the oto-rhino-laryngological region lack spindles whilst their direct antagonists possess them. Amongst the muscles of the external and middle ear, the soft palate and the larynx having opposite actions, there is in each case one muscle which does not have any spindles. These muscles then have only motor innervation. The muscles which have neuro-muscular spindles are innervated by nerves composed of extra- and intrafusal motor fibres and proprioceptive fibres. The neuro-muscular spindles play a servo-braking role in the muscle where they occur. They oppose then a certain passive elongation of the muscle. At the same time and in this manner, they contribute in controlling and restraining the action of the muscles or of their opponents. This role is particularly important for the various muscles of the oto-rhinolaryngological region and is all the more important since the amplitude of the movements which they cause is very weak. The presence of these spindles increases also the sensitivity and the delicacy of the desired movement, for the behaviour of these muscles is very special.