Dust Source Activation Frequency in the Horn of Africa

Mineral dust aerosols play an important role in Earth's climate through interactions with incoming solar radiation, clouds, and the atmosphere. However, dust sources in the Horn of Africa (HoA) and controls on their activation are poorly documented. Here, we use fifteen-minute Meteosat Second Generation Spinning Enhanced Visible and Infrared Imager dust index images to identify HoA dust source areas and to quantify their activation frequency in 1° × 1° resolution from 2006 to 2010. Around half of all recorded dust events occur in boreal summer, mostly between 8:00 and 16:00 local time. They are driven by meso- to regional scale meteorological mechanisms including the breakdown of the nocturnal low-level jets, land-sea breezes, and haboobs. By far the most dust-active region in the HoA is the Afar Triangle (>77% of all recorded dust events) which features the Afar and Danakil depressions and is fed by the Awash River. Despite experiencing strong and persistent southwest summer monsoon winds, dust activation on the Somali Peninsula is less significant. A composite of our map with data for North Africa and westernmost Asia shows that the HoA is a striking latitudinal anomaly with dust activation extending deep into the equatorial belt. Our data also reveal that dust activation is unusually seasonal with ∼40% of events occurring in June and July. Our findings show that aridity and mean wind strength alone are poor predictors of dust activation and underscore the strong control exerted by the availability of readily deflated unconsolidated riverine and lacustrine sediments

Assessing the impact of diagenesis on foraminiferal geochemistry from a low latitude, shallow-water drift deposit

Due to their large heat and moisture storage capabilities, the tropics are fundamental in modulating both regional and global climate. Furthermore, their thermal response during past extreme warming periods, such as super interglacials, is not fully resolved. In this regard, we present high-resolution (analytical) foraminiferal geochemical (δ18O and Mg/Ca) records for the last 1800 kyr from the shallow (487 m) Inner Sea drift deposits of the Maldives archipelago in the equatorial Indian Ocean. Considering the diagenetic susceptibility of these proxies, in carbonate-rich environments, we assess the integrity of a suite of commonly used planktonic and benthic foraminifera geochemical datasets (Globigerinoides ruber (white), Globigerinita glutinata (with bulla), Pulleniatina obliquiloculata (with cortex) and Cibicides mabahethi) and their use for future paleoceanographic reconstructions. Using a combination of spot Secondary Ion Mass Spectrometer, Electron Probe Micro-Analyzer and Scanning Electron Microscope image data, it is evident that authigenic overgrowths are present on both the external and internal test (shell) surfaces, yet the degree down-core as well as the associated bias is shown to be variable across the investigated species and proxies. Given the elevated authigenic overgrowth Mg/Ca (∼12–22 mmol/mol) and δ18O values (closer to the benthic isotopic compositions) the whole-test planktonic G. ruber (w) geochemical records are notably impacted beyond ∼627.4 ka (24.7 mcd). Yet, considering the setting (i.e. bottom water location) for overgrowth formation, the benthic foraminifera δ18O record is markedly less impacted with only minor diagenetic bias beyond ∼790.0 ka (28.7 mcd). Even though only the top of the G. ruber (w) and C. mabahethi records (whole-test data) would be suitable for paleo-reconstructions of absolute values (i.e. sea surface temperature, salinity, seawater δ18O), the long-term cycles, while dampened, appear to be preserved. Furthermore, planktonic species with thicker-tests (i.e. P. obliquiloculata (w/c)) might be better suited, in comparison to thinner-test counter-parts (i.e. G. glutinata (w/b), G. ruber (w)), for traditional whole- test geochemical studies in shallow, carbonate-rich environments. A thicker test equates to a smaller overall bias from the authigenic overgrowth. Overall, if the diagenetic impact is constrained, as done in this study, these types of diagenetically altered geochemical records can still significantly contribute to studies relating to past tropical seawater temperatures, latitudinal scale ocean current shifts and South Asian Monsoon dynamics

Three North African dust source areas and their geochemical fingerprint

North Africa produces more than half of the world’s atmospheric dust load. Once entrained 24 into the atmosphere, this dust poses a human health hazard locally. It also modifies the 25 radiative budget regionally, and supplies nutrients that fuel primary productivity across the 26 North Atlantic Ocean and as far afield as the Amazonian Basin. Dust accumulation in deep 27 sea and lacustrine sediments also provides a means to study changes in palaeoclimate, 28 particularly those associated with rainfall climate change. Systematic analysis of satellite 29 imagery has greatly improved our understanding of the trajectories of long-range North 30 African dust plumes, but our knowledge of the dust-producing source regions and our ability 31 to fingerprint their contribution to these export routes is surprisingly limited. Here we 32 report new radiogenic isotope (Sr and Nd) data for sediment samples from known dust33 producing substrates (dried river and lakes beds), integrate them with published isotope 34 data and weight them for dust source activation. We define three isotopically distinct 35 preferential dust source areas (PSAs): a Western, a Central and an Eastern North African 36 PSA. More data are needed, particularly from the Western PSA, but our results show a 37 change in PSA dust source composition to more radiogenic Nd- and less radiogenic Sr38 isotope values from west to east, in line with the overall decreasing age of the underlying 39 bedrock. Our data reveal extreme isotopic heterogeneity within the Chadian region of the 40 Central PSA, including an extremely distinctive geochemical fingerprint feeding the Bodélé 41 Depression, the most active dust source on Earth. Our new analysis significantly improves 42 the reliability by which windblown dust deposits can be geochemically fingerprinted to their 43 distant source regions

Correction to:A two million year record of low-latitude aridity linked to continental weathering from the Maldives (Progress in Earth and Planetary Science, (2018), 5, 1, (86), 10.1186/s40645-018-0238-x)

In the original version of this article (Kunkelova et al. 2018), published on 18 December 2018, there was 1 error in the author name of Dr. Yu

A two million year record of low-latitude aridity linked to continental weathering from the Maldives

Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ 18 O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition. The Correction to this article has been published in Progress in Earth and Planetary Science 2019 6:21 - https://doi.org/10.1186/s40645-019-0259-

A two million year record of low-latitude aridity linked to continental weathering from the Maldives

Tem uma correção em http://hdl.handle.net/10400.1/12390Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ18O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition.SFRH/BPD/96960/2013; PTDC/MAR-PRO/3396/2014info:eu-repo/semantics/publishedVersio

Supplementary Data for the article 'Dust source activation frequency in the Horn of Africa'

Supplementary Table 1. Dust source activation data from the Horn of Africa from &#xFEFF;MSG SEVIRI instrument spanning between 1st of March 2006 and 28th of February 2010. Data includes location of dust activation (longitude and latitude), cloud cover (clear-sky conditions are labelled as 1, clouded conditions as 2) and time of the onset of dust events from 0 to 24 at 1-hour intervals in UTC </span

Supplementary information for the article &#39;Dust sources in Westernmost Asia have a different geochemical fingerprint to those in the Sahara&#39;

Kunkelova, T., Crocker, A.J., Jewell, A.M., Breeze, P.S., Drake, N.A., Cooper, M.J., Milton, J.A., Hennen, M., Shahgedanova, M., Petraglia, M.D., Wilson, P.A., 2022. Dust sources in Westernmost Asia have a different geochemical fingerprint to those in the Sahara. Quat. Sci. Rev. 294, 107717. https://doi.org/10.1016/j.quascirev.2022.107717</span

Dust sources to the Arabian Sea and their record of continental hydroclimate

Mineral dust plays an important role in Earth’s climate as it affects radiation budgets, regional hydroclimates and provides nutrients to the Arabian Sea and further afield. Dust accumulating in deep sea sediment has the potential to provide long uninterrupted records of past changes in hydroclimate. However, to read these records properly it is important to be able to trace these dust deposits to their origin. Dust records from the Arabian Sea have long been used to reconstruct past changes in continental hydroclimate. However, this ocean basin is encircled by many arid and dust-producing regions and its dust record has been variously attributed to East Africa, the Arabian Peninsula, Mesopotamia and further east into southwest Asia. This thesis is composed of three main inter-related studies. In the first, I use geochemical methods (Sr and Nd isotopes) to fingerprint major dust producing regions on the Arabian Peninsula and southwest Asia and distinguish them from those of Africa. In the second, I employ high-resolution remote sensing observations over a four-year interval to map dust activation frequency in the Horn of Africa. Lastly, I report the results of a dust-based palaeo study of hydroclimate change from the western Arabian Sea covering the middle Pliocene and late Quaternary