Changes in sediment supply and caliber during the last ~130 ka have resulted in a complex architectural evolution of the Y channel system on the western Niger Delta slope. This evolution consists of four phases, each with documented or inferred changes in sediment supply. Phase 1 flows created wide (1,000 m), low-sinuosity (1.1) channel forms with lateral migration and little to no aggradation. During Phase 2, the Y channel system began to aggrade, creating more narrow (300 m) and sinuous (1.4) channel forms with many meander cutoffs. This system was abandoned at ~ 130 ka, perhaps related to rapid relative sea-level rise during MIS (Marine Isotope Stage) 5. Phase 3 flows were mud-rich and deposited sediment on the outer bends of the channel form, resulting in the narrowing (to 250 m), straightening (to a sinuosity of 1.22), and aggradation of the Y channel system. Renewed influx of sand into the Y channel system occurred with Phase 4 at ~ 50 ka, during MIS 3 sea-level fall. The onset of Phase 4 is marked by the initiation of the Y′ tributary channel, which re-established sand deposition in the Y channel system. Flows entering the Y channel from the Y′ channel were underfit, resulting in inner levee deposition that is most prevalent on outer banks, acting to further straighten (1.21) and narrow (to 200 m wide) the Y channel. The inner levees accumulated quickly as the flows sought equilibrium, with deposition rates > 200 cm/ky. Marked by the presence of the last sand bed, abandonment occurred at ~19 ka in the Y channel and ~15 ka in the Y′ channel and is likely related to progressive abandonment due to shelf-edge delta avulsion and/or progressive sea level rise associated with Melt Water Pulse 1-A. The muddy, 5-meter-thick Holocene layer has thickness variations that mimic those seen in the sandy part of Phase 4, suggesting that dilute, muddy flows continue to affect the modern Y channel system. This unique dataset allows us to unequivocally link changes in submarine channel architecture to variations in sediment supply and caliber. Changes in the updip sediment routing system (i.e. the channel "plumbing") are shown to have profound implications for submarine channel architecture and reservoir connectivity.

15Near-seafloor core and seismic-reflection data from the western Niger Delta continental 16 slope document the facies, architecture, and evolution of submarine channel and intraslope 17 submarine fan deposits. The submarine channel enters an 8 km long x 8 km wide intraslope 18 basin, where more than 100 m of deposits form an intraslope submarine fan. Lobe deposits in the 19 intraslope submarine fan show no significant downslope trend in sand presence or grain size, 20 indicating that flows were bypassing sediment through the basin. This unique dataset indicates 21 that intraslope lobe deposits may have more sand-rich facies near lobe edges than predicted by 22 traditional lobe facies models, and that thickness patterns in intraslope submarine fans do not 23 necessarily correlate with sand presence and/or quality. 24Core and radiocarbon age data indicate that sand beds progressively stack southward 25 during the late Pleistocene, resulting in the compensation of at least two lobe elements. The 26 youngest lobe element is well characterized by core data and is sand-rich, ~ 2 km wide x 6 km 27 long, > 1 m thick, and was deposited rapidly over ca. 4,000 yr, from 18-14 ka. Sand beds 28Jobe et al. -Bed compensation on an intraslope submarine fan, Nigeria 2 forming an earlier lobe element were deposited on the northern part of the fan from ca. 25 to 18 29 ka. Seafloor geomorphology and amplitudes from seismic reflection data confirm the location 30

The role of Atlantic Meridional Overturning Circulation (AMOC) as the driver of Dansgaard-Oeschger (DO) variability that characterized Marine Isotope Stage 3 (MIS 3) has long been hypothesized. Although there is ample proxy evidence suggesting that DO events were robust features of glacial climate, there is little data supporting a link with AMOC. Recently, modeling studies and subsurface temperature reconstructions have suggested that subsurface warming across the tropical North Atlantic can be used to fingerprint a weakened AMOC during the deglacial because a reduction in the strength of the western boundary current allows warm salinity maximum water of the subtropical gyre to enter the deep tropics. To determine if AMOC variability played a role during the DO cycles of MIS 3, we present new, high-resolution Mg/Ca and δ 18 O records spanning 24-52 kyr from the near-surface dwelling planktonic foraminifera Globigerinoides ruber and the lower thermocline dwelling planktonic foraminifera Globorotalia truncatulinoides in Southern Caribbean core VM12-107 (11.33°N, 66.63°W, 1079 m depth). Our subsurface Mg/Ca record reveals abrupt increases in Mg/Ca ratios (the largest equal to a 4°C warming) during the interstadial-stadial transition of most DO events during this period. This change is consistent with reconstructions of subsurface warming events associated with cold events across the deglacial using the same core. Additionally, our data support the conclusion reached by a recently published study from the Florida Straits that AMOC did not undergo significant reductions during Heinrich events 2 and 3. This record presents some of the first high-resolution marine sediment derived evidence for variable AMOC during MIS 3.

24 Widespread drought characterized the Heinrich 1 and Younger Dryas cold periods 25 of the last deglacial throughout much of Africa, causing large increases in dust 26 emissions from the Sahara and Sahel. At the same time, increases in wind strength 27 may have also contributed to dust flux, making it difficult to interpret dust records 28 alone as reflecting changes in rainfall over the region. The Niger River has the third 29 largest drainage basin in Africa and drains most of the Sahara and Sahel and thus 30 preserves and propagates climatic signals. Here, we present new reconstructions of 31 Niger Delta sea surface salinity and Niger River discharge for the last 20,000 years 32 in order to more accurately reconstruct the onset of the Western African Monsoon 33 system. Based on calculated  18 O SEAWATER ( 18 O SW ) and measured Ba/Ca ratios in 34 planktonic foraminifera, these new records reflect changes in sub-Saharan 35 precipitation across the Niger River Basin in West Africa and reveal that the West 36 African Monsoon system began to intensify several thousand years after the 37 equatorial Monsoon system in Central Africa. We also present new records of 38 primary productivity in the Niger Delta that are related to wind-driven upwelling 39 and show that productivity is decoupled from changes in Niger River discharge. 40 Our results suggest that wind strength, rather than changes in monsoon moisture, 41 was the primary driver of dust emissions from the Sahara and Sahel across the last 42 deglaciation. 43 44

Multiple lines of evidence show that cold stadials in the North Atlantic were accompanied by both reductions in Atlantic Meridional Overturning Circulation (AMOC) and collapses of the West African Monsoon (WAM). Although records of terrestrial change identify abrupt WAM variability across the deglaciation, few studies show how ocean temperatures evolved across the deglaciation. To identify the mechanism linking AMOC to the WAM, we generated a new record of subsurface temperature variability over the last 21 kyr based on Mg/Ca ratios in a sub-thermocline dwelling planktonic foraminifera in an Eastern Equatorial Atlantic (EEA) sediment core from the Niger Delta. Our subsurface temperature record shows abrupt subsurface warming during both the Younger Dryas (YD) and Heinrich Event 1. We also conducted a new transient coupled ocean-atmosphere model simulation across the YD that better resolves the western boundary current dynamics and find a strong negative correlation between AMOC strength and EEA subsurface temperatures caused by changes in ocean circulation and rainfall responses that are consistent with the observed WAM change. Our combined proxy and modeling results provide the first evidence that an oceanic teleconnection between AMOC strength and subsurface temperature in the EEA impacted the intensity of the WAM on millennial time scales.