Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

Abstract

Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. O rogenesis reflects the balance of crustal material entering a mountain belt to undergo shortening and uplift versus material leaving the orogen through exhumation, erosion, and sediment transport (1-5). Perturbations in the influx/efflux from the orogen are expected to result in predictable changes in deformation within the orogen as it attempts to reestablish equilibrium (3). The long-term sink for sediment transported out of mountain belts is often in the deep sea, particularly in large submarine fans where sediments accumulate at anomalously high rates (>10 cm/ky) compared with deep-sea pelagic sedimentation (6-8). Even higher sedimentation rates (>100 cm/ky) proximal to glacially eroded regions (9-14) imply that wet-based glaciers are extremely efficient agents of erosion. Observations and modeling have argued that erosion rates can influence tectonic processes (15)(16)(17)(18)(19), but the timescales of adjustment, and the role of landscape disequilibrium, remain unclear. For example, exceptionally high local sedimentation rates (100-1000 cm/ky) recorded on the century timescale (13) SignificanceIn coastal Alaska and the St. Elias orogen, over the past 1.2 million years, mass flux leaving the mountains due to glacial erosion exceeds the plate tectonic input. This...

The Impact of Hydro Climatic Variability on Water Resources of Lake Chad Hydro Graphic Basin

“…: total observed flows of two terms immediately preceding the term t. X (t+2) and X (t+1) : observed rainfall totals of two terms immediately following the term t. The first two [X (1) , X (2) ] and the last two [X (n-1) , X (n) ] terms of the series are calculated using the following expressions (being the size of the series): (1) +0.46X (2) …”

“…Depending on the alternations between the wet and dry periods, Lake Chad extends or shrinks, but from 1970 to the present day, the decline of the waters has accelerated, corresponding to the aridity and the advance of the desert. Climate change and increased anthropogenic pressure on earth-atmosphere interactions affect water quantity, quality, and waterrelated processes, such as sediment yield, on local, regional, and global scales [1].…”

Quaternary radiolarian biostratigraphy in the subarctic northeastern Pacific (IODP Expedition 341 Site U1417) and synchroneity of bioevents across the North Pacific

“…In order to clarify the relationship between tectonic and climate changes during the Neogene, Expedition 341 of the Integrated Ocean Drilling Program (IODP) retrieved sediment cores at five sites off the southern Gulf of Alaska (northeastern Pacific) between 29 May and 29 July 2013 (sites U1417 to U1421) (Jaeger et al, 2014;Gulick et al, 2015). The deep-sea sediments collected at Site U1417 span the time interval from the Pleistocene to the Miocene (Jaeger et al, 2014).…”

Water Resource Variability and Climate Change

“…Climate change and increased anthropogenic pressure on earth-atmosphere interactions affect water quantity, quality, and water-related processes, such as sediment yield, on local, regional, and global scales [1][2][3]. Recent decades have seen continuously increasing temperatures in most parts of the world, and changes in precipitation patterns have increased the frequency of extreme climate events such as drought and flooding [4].…”