Carbonate drifts as marine archives of aeolian dust (Santaren Channel, Bahamas)

Abstract

Sediment data from the Bahamian Santaren carbonate drift reveal the variability of trans-Atlantic Saharan dust transport back to about 100 ka BP (Marine Isotope Stage 5Á3) and demonstrate that carbonate drifts are a valuable pelagic archive of aeolian dust flux. Carbonate drift bodies are common around tropical carbonate platforms; they represent large-scale accumulations of ocean-current transported material, which originates from the adjacent shallow-water carbonate factory as well as from pelagic production, i.e. periplatform ooze. Subordinately, there is a clay-size to silt-size non-carbonate fraction, which typically amounts to less than 10% of the sediment volume and originates from aeolian and fluvial input. Sedimentation rates in the 5Á42 m long core GeoHH-M95-524 recovered 25 km west of Great Bahama Bank in the Santaren Channel ranges from 1Á5 to 24Á5 cm ka À1 with lowest values during the last glacial lowstand and highest values following platform re-flooding around 8 ka BP. These sedimentation rates imply that carbonate drifts have not only the potential to resolve long-term environmental changes on orbital timescales, but also millennial to centennial fluctuations during interglacials. The sediment core has been investigated with the aim of characterizing the lithogenic dust fraction. Laboratory analyses included X-ray fluorescence core scanning, determination of carbonate content and grain-size analyses (of bulk and terrigenous fraction), as well as visual inspections of the lithogenic residue; the age model is based on oxygen isotopes and radiocarbon ages. Data show that the input of aeolian dust in the periplatform ooze as indicated by Ti/Al and Fe/Al element ratios abruptly increases at 57 ka BP, stays elevated during glacial times, and reaches a Holocene minimum around 6Á5 ka BP, contemporary to the African Humid Period. Subsequently, there is a gradual increase in dust flux which almost reaches glacial levels during the last centuries. Grain-size data show that the majority of dust particles fall into the fine silt range (below 10 lm); however, there is a pronounced coarse dust fraction in the size range up to 63 lm and individual 'giant' dust particles are up to 515 lm in size. Total dust flux and the relative amounts of fine and coarse dust are decoupled. The time-variable composition of the grain-size spectrum is interpreted to reflect different dust transport mechanisms: fine dust particles are delivered by the trade winds and the geostrophic winds of the Saharan Air Layer, whereas coarse dust particles travel with convective storm systems. This mode of transport ensures continuous re-suspension of large particles and 1386 results in a prolonged transport. In this context, grain-size data from the terrigenous fraction of carbonate drifts provide a measure for past coarse dust transport, and consequently for the frequency of convective storm systems over the dust source areas and the tropical Atlantic.

Marine carbonate factories: Review and update

“…McNeill et al, 2000;Bauch et al, 2011). Another source of terrestrial material might be windblown dust which may easily cross oceans (Stuut et al, 2005;Lindhorst et al, 2019). For the Bahamas, Swart et al (2014) proposed that atmospheric dust acted as fertilizer, stimulating carbonate production in the shallow waters of the Great Bahama Bank.…”

“…McNeill et al ., 2000; Bauch et al ., 2011). Another source of terrestrial material might be windblown dust which may easily cross oceans (Stuut et al ., 2005; Lindhorst et al ., 2019). For the Bahamas, Swart et al .…”

Strontium isotope dating influenced by Rubidium contamination from terrestrial material: A case study from the Cenozoic dolomite in the Xisha Islands, South China Sea

“…Given that terrestrial materials (mainly quartz, feldspar and clay minerals) are commonly rich in Al, Ti and K‐bearing minerals (Wang & Li, 2009; Muhs et al ., 2014), the correlations between Al, Ti and K in marine carbonate sediments have generally been attributed to wind‐blown and/or riverine sources (e.g. Stuut et al ., 2005; Lindhorst et al ., 2019; Reijmer, 2021). On East Island in the Xisha Islands (Fig.…”