Milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr BP

Kutzbach, John E.; Street-Perrott, F. Alayne

doi:10.1038/317130a0

Cited by 633 publications

(257 citation statements)

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“…This implies that dust flux maxima corresponded to minimum northern hemisphere summer insolation levels (at the precession band) associated with weak summer monsoons that resulted in less vegetation in the South Sahara and Sahel zone. This result agrees with modeling studies [Kutzbach, 1981;Prell and Kutzbach, 1987] and with paleoclimatic evidence from the Saharan and Indian subcontinent [Street and Grove, 1979;Rossignol-Strick, 1983;Kutzbach and Street-Perrott, 1985;Pokras and Mix, 1985]. We fine-tuned the dust flux maxima directly to summer insolation minima (July), assuming no phase differences (Figure 4).…”

Section: Composite Depth Sectionssupporting

confidence: 86%

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659

Tiedemann¹,

Sarnthein²,

Shackleton³

1994

Paleoceanography

673

485

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Abstract. High-resolution benthic oxygen isotope and dust flux records from Ocean Drilling Program site 659 have been analyzed to extend the astronomically calibrated isotope timescale for the Atlantic from 2.85 Ma back to 5 Ma. Spectral analysis of the o 1 BO record indicates that the 41-kyr period of Earth's orbital obliquity dominates the Pliocene record. This is shown to be true regardless of fundamental changes in the Earth's climate during the Pliocene. However, the cycles of Sahelian aridity fluctuations indicate a shift in spectral character near 3 Ma. From the early Pliocene to 3 Ma, the periodicities were dominantly precessional (19 and 23 kyr) and remained strong until1.5 Ma. Subsequent to 3 Ma, the variance at the obliquity period (41 kyr) increased. The timescale tuned to precession suggests that the Pliocene was longer than previously estimated by more than 0.5 m.y. The tuned ages for the magnetic boundaries Gauss/Gilbert and Top Cochiti are about 6-8% older than the ages of the conventional timescale. A major phase of Pliocene northern hemisphere ice growth occurred between 3.15 Ma and 2.5Ma. This was marked by a gradual increase in glacial Atlantic o 1 BO values of 1o/oo and an increase in amplitude variations by up to 1.5o/oo, much larger than in the Pacific deepwater record (site 846). The first maxima occured in cold stages G6-96 between 2.7 Ma and 2.45 Ma. Prior to 3 Ma, the isotope record is characterized by predominantly low amplitude fluctuations(< 0.7o/oo.). When obliquity forcing was at its minimum between 4.15 and 3.6 Ma and during the Kaena interval, o 18 0 amplitude fluctuations were minimal. From 4.9 to 4.3 Ma, the o 18 0 values decreased by about 0.5o/oo, reaching a long-term minimum at 4.15 Ma, suggesting higher deepwater temperatures or a deglaciation. Deepwater cooling and/or an increase in ice volume is indicated by a series of short-term o 1 BO fluctuations between 3.8 and 3.6 Ma.

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Section: Composite Depth Sectionssupporting

confidence: 86%

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659

Tiedemann¹,

Sarnthein²,

Shackleton³

1994

Paleoceanography

673

485

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“…Reviews of lake-level change within the southern Sahara and Sahel indicate additional millennial to centennial changes superimposed on the broad pattern of increase and subsequent decrease in humidity since the LGM (6). These three scenarios, (i) abrupt onset and termination, (ii) gradual change, and (iii) a broad trend with shorter-term variability, are supported to a greater or lesser extent by climate models in which an enhanced WAM is linked to summer-season insolation in the Northern Hemisphere, which peaked around 10 ka and then gradually declined (7)(8)(9). Abrupt changes in North African climate can be simulated by biogeophysical feedbacks (7), whereas a gradual change in rainfall is simulated by a coupled transient simulation model (9), where vegetation feedbacks are muted and more localized.…”

Section: West African Monsoon Dynamicsmentioning

confidence: 79%

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

Armitage

Bristow

Drake

2015

Proc. Natl. Acad. Sci. U.S.A.

129

116

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From the deglacial period to the mid-Holocene, North Africa was characterized by much wetter conditions than today. The broad timing of this period, termed the African Humid Period, is well known. However, the rapidity of the onset and termination of the African Humid Period are contested, with strong evidence for both abrupt and gradual change. We use optically stimulated luminescence dating of dunes, shorelines, and fluviolacustrine deposits to reconstruct the fluctuations of Lake Mega-Chad, which was the largest pluvial lake in Africa. Humid conditions first occur at ∼15 ka, and by 11.5 ka, Lake Mega-Chad had reached a highstand, which persisted until 5.0 ka. Lake levels fell rapidly at ∼5 ka, indicating abrupt aridification across the entire Lake Mega-Chad Basin. This record provides strong terrestrial evidence that the African Humid Period ended abruptly, supporting the hypothesis that the African monsoon responds to insolation forcing in a markedly nonlinear manner. In addition, Lake Mega-Chad exerts strong control on global biogeochemical cycles because the northern (Bodélé) basin is currently the world’s greatest single dust source and possibly an important source of limiting nutrients for both the Amazon Basin and equatorial Atlantic. However, we demonstrate that the final desiccation of the Bodélé Basin occurred around 1 ka. Consequently, the present-day mode and scale of dust production from the Bodélé Basin cannot have occurred before 1 ka, suggesting that its role in fertilizing marine and terrestrial ecosystems is either overstated or geologically recent.

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“…1) 62 remains a highly debated issue [e.g. Kuper and Kröpelin, 2006;Costa et al, 2014; 63 deMenocal et al, 2000; Kuhlmann et al, 2004; Tierney and 64 deMenocal, 2013;Tierney et al, 2008;Junginger et al, 2014; Weldeab 65 et al, 2014;Marshall et al, 2011;Kutzbach and Street-Perrott, 1985; Claussen et al, 66 1999]. In East Africa, the role of non-linear biogeophysical climate feedbacks is also 67 debated with recent studies concluding that non-linear biogeophysical climate feedbacks 68 4 between precipitation and vegetation are absent , that a nonlinear 69 convection feedback associated with Indian Ocean SST could be an important contributor 70 to rainfall variability [Tierney and deMenocal, 2013], or that a non-linear change in 71 vegetation and sediment erosion occurred in the Early Holocene without a significant 72 decrease in precipitation [Blanchet et al, 2014].…”

mentioning

confidence: 99%

Hydroclimate variability in the Nile River Basin during the past 28,000 years

Castañeda

Schouten

Pätzold

et al. 2016

Earth and Planetary Science Letters

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13It has long been known that extreme changes in North African hydroclimate occurred 14 during the late Pleistocene yet many discrepancies exist between sites regarding the timing, 15 duration and abruptness of events such as Heinrich Stadial (HS) 1 and the African Humid 16Period (AHP). The hydroclimate history of the Nile River is of particular interest due to its 17 lengthy human occupation history yet there are presently few continuous archives from the 18 Nile River corridor, and pre-Holocene studies are rare. Here we present new organic and 19 inorganic geochemical records of Nile Basin hydroclimate from an eastern Mediterranean 20 (EM) Sea sediment core spanning the past 28 ka BP. Our multi-proxy records reflect the 21 fluctuating inputs of Blue Nile versus White Nile material to the EM Sea in response to 22 2 gradual changes in local insolation and also capture abrupt hydroclimate events driven by 23 remote climate forcings, such as HS1. We find strong evidence for extreme aridity within 24 the Nile Basin evolving in two distinct phases during HS1, from 17.5 to 16 ka BP and from 25 16-14.5 ka BP, whereas peak wet conditions during the AHP are observed from 9-7 ka BP. 26We find that zonal movements of the Congo Air Boundary (CAB), and associated shifts in 27 the dominant moisture source (Atlantic versus Indian Ocean moisture) to the Nile Basin, 28 likely contributed to abrupt hydroclimate variability in northern East Africa during HS1 29 and the AHP as well as to non-linear behavior of hydroclimate proxies. We note that 30 different proxies show variable gradual and abrupt responses to individual hydroclimate 31 events, and thus might have different inherent sensitivities, which may be a factor partially 32 contributing to the controversy surrounding the abruptness of past events such as the AHP. Introduction 40The paleoclimate history of the Nile River valley in East Africa is of interest due to its 41 rich history of human occupation (Vermeersch and Van Neer, 2015). Relationships 42 between climate and the distribution of settlements on the Nile River corridor have long 43 been recognized and it is hypothesized that extreme changes in African hydroclimate 44 helped shape the growth and led to the decline of numerous complex societies [Kuper and 45 3 Kröpelin, 2006]. One of the most dramatic changes in North African hydroclimate, the so-46 called African Humid Period (AHP) [deMenocal et al., 2000], occurred during the early 47Holocene when increased rainfall allowed vegetation, lakes and human populations to 48 occupy a "green Sahara", a region that today is a hyperarid desert [Kuper and Kröpelin, 49 2006]. Variability in Nile River flow also played an important role in shaping Egypt's 50 civilizations with the collapse of the Old Kingdom at 4,160 years before present, attributed 51 to a 30 year absence of annual Nile flooding [Stanley et al., 2003]. Although lacking direct 52 evidence, it is hypothesized that HS1, which is recognized as an extreme and widespread 53 drought in North Afri...

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Milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr BP

Cited by 633 publications

References 34 publications

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

Hydroclimate variability in the Nile River Basin during the past 28,000 years

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Milankovitch forcing of fluctuations in the level of tropical lakes from 18 to 0 kyr BP

Cited by 633 publications

References 34 publications

Astronomic timescale for the Pliocene Atlantic δ18O and dust flux records of Ocean Drilling Program Site 659

Astronomic timescale for the Pliocene Atlantic δ18O and dust flux records of Ocean Drilling Program Site 659

West African monsoon dynamics inferred from abrupt fluctuations of Lake Mega-Chad

Hydroclimate variability in the Nile River Basin during the past 28,000 years

Contact Info

Product

Resources

About

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659

Astronomic timescale for the Pliocene Atlantic δ¹⁸O and dust flux records of Ocean Drilling Program Site 659