Showing papers by "Gerald H. Haug published in 2012"

Development and Disintegration of Maya Political Systems in Response to Climate Change

Abstract: The role of climate change in the development and demise of Classic Maya civilization (300 to 1000 C.E.) remains controversial because of the absence of well-dated climate and archaeological sequences. We present a precisely dated subannual climate record for the past 2000 years from Yok Balum Cave, Belize. From comparison of this record with historical events compiled from well-dated stone monuments, we propose that anomalously high rainfall favored unprecedented population expansion and the proliferation of political centers between 440 and 660 C.E. This was followed by a drying trend between 660 and 1000 C.E. that triggered the balkanization of polities, increased warfare, and the asynchronous disintegration of polities, followed by population collapse in the context of an extended drought between 1020 and 1100 C.E.

Subsurface tropical Pacific nitrogen isotopic composition of nitrate: Biogeochemical signals and their transport

Abstract: [1] We report measurements of the nitrogen isotopic composition of nitrate (the δ15N of NO3−) across the equatorial Pacific, for zonal transects from 165°E to 95°W and meridional transects across 95° and 110°W The δ15N of NO3− is similar in the equatorial thermocline (≈100 m) and intermediate depth waters (≈150 to 600 m), averaging (71 ± 03)‰ and (71 ± 01)‰, respectively These values are more than 2‰ higher than subthermocline waters of the Southern and Atlantic Oceans and are ≈1‰ higher than putative source waters in the high latitude South Pacific (Subantarctic Mode Water, SAMW) The combined constraints of nitrate concentration and δ15N of NO3−in the equatorial Pacific require (1) lateral exchange between the high-latitude source waters and the zones of denitrification in the eastern tropical Pacific and (2) the accumulation of remineralized nutrients at depth The zonal uniformity of the subsurface equatorial Pacificδ15N of NO3− indicates rapid transport within the equatorial zone, which works to homogenize the δ15N of NO3− across the Pacific basin Against this backdrop of high δ15N of NO3−in the tropical Pacific, we find a discrete off-equatorial core of lowerδ15N of NO3− (55 ± 03)‰ concentrated at 5°S and 150 to 200 m along the 110° and 95°W transects and in apparent association with the Southern Subsurface Counter Current (SSCC) We propose that the remineralized products of nitrogen fixation, at the source of the SSCC in the western south Pacific, are the origin of the low δ15N of NO3− in these waters

Impact of Indus River discharge on productivity and preservation of organic carbon in the Arabian Sea over the twentieth century

Abstract: Marine high-productivity zones along the continents are of great economic importance, and they account for most organic carbon burial. The carbon cycle in many coastal zones is influenced by the sediments and dissolved nutrients introduced by rivers. However, there is little direct evidence for a regional marine response to changes in river dynamics. Here we present a suite of high-resolution records of organic and inorganic paleoceanographic proxies, which together demonstrate that past changes in Indus River discharge have strongly affected productivity patterns in the coastal northeastern Arabian Sea. Anthropogenic activity, including the building of dams and irrigation facilities during the past century, has drastically decreased the discharge rate of the Indus River. Between A.D. 1890 and 1998, the period over which this reduction occurred, primary productivity off the Pakistan coast seems to have decreased by more than one-third. Over the same period, the regional oxygen minimum zone weakened, increasing the supply of oxygen to the sediments, leaving the expected imprint on a suite of redox-sensitive elements and reducing the preservation of organic matter.

Decadal- to centennial-scale tropical Atlantic climate variability across a Dansgaard-Oeschger cycle

Abstract: [1] The patterns and forcing mechanisms of climate variability on decadal to centennial time scales represent a major void in our current understanding of Earth's climate system. Furthermore, the response of the low latitudes to abrupt climate change is also not well understood, as most high-resolution paleoclimate studies are from midlatitudes and high latitudes. This study explores the tropical Atlantic response to a Dansgaard-Oeschger cycle (Interstadial 12) using ultra-high resolution (∼2–3 years) foraminiferal census data from Cariaco Basin sediments. The interpretation of the abundance records for the onset of Interstadial 12 is complicated by the competing effects of rising sea level on Ekman-induced upwelling within the Cariaco Basin and migrating Intertropical Convergence Zone–associated variations in trade wind location and fluvial nutrient delivery to the basin. The foraminiferal abundance records for the latter part of the interstadial suggest a southerly shift in the average annual position of the Intertropical Convergence Zone that acted to enhance upwelling and productivity within the Cariaco Basin. Sea level eventually reached a critical point in the transition back to stadial conditions that led to upwelling of nutrient-depleted waters and a decline in productivity within the basin. Spectral analyses of theGlobigerina bulloidesabsolute abundance records reveal significant variability ranging from subdecadal- to centennial-scale. Atlantic multidecadal-scale climate variability is only evident in the warmest interval of Interstadial 12, suggesting that variability on this scale may only operate during warm climate periods, something that has significant implications for modern and near-future climate variability.

Sea surface temperatures did not control the first occurrence of Hudson Strait Heinrich Events during MIS 16

Abstract: [1] Hudson Strait (HS) Heinrich Events, ice-rafting events in the North Atlantic originating from the Laurentide ice sheet (LIS), are among the most dramatic examples of millennial-scale climate variability and have a large influence on global climate. However, it is debated as to whether the occurrence of HS Heinrich Events in the (eastern) North Atlantic in the geological record depends on greater ice discharge, or simply from the longer survival of icebergs in cold waters. Using sediments from Integrated Ocean Drilling Program (IODP) Site U1313 in the North Atlantic spanning the period between 960 and 320 ka, we show that sea surface temperatures (SSTs) did not control the first occurrence of HS Heinrich(-like) Events in the sedimentary record. Using mineralogy and organic geochemistry to determine the characteristics of ice-rafting debris (IRD), we detect the first HS Heinrich(-like) Event in our record around 643 ka (Marine Isotope Stage (MIS) 16), which is similar as previously reported for Site U1308. However, the accompanying high-resolution alkenone-based SST record demonstrates that the first HS Heinrich(-like) Event did not coincide with low SSTs. Thus, the HS Heinrich(-like) Events do indicate enhanced ice discharge from the LIS at the end of the Mid-Pleistocene Transition, not simply the survivability of icebergs due to cold conditions in the North Atlantic.

carbon in the Arabian Sea over the twentieth century Impact of Indus River discharge on productivity and preservation of organic

Abstract: Marine high-productivity zones along the continents are of great economic importance, and they account for most organic carbon burial. The carbon cycle in many coastal zones is infl u-enced by the sediments and dissolved nutrients introduced by rivers. However, there is little direct evidence for a regional marine response to changes in river dynamics. Here we present a suite of high-resolution records of organic and inorganic paleoceanographic proxies, which together demonstrate that past changes in Indus River discharge have strongly affected pro-ductivity patterns in the coastal northeastern Arabian Sea. Anthropogenic activity, including the building of dams and irrigation facilities during the past century, has drastically decreased the discharge rate of the Indus River. Between A.D. 1890 and 1998, the period over which this reduction occurred, primary productivity off the Pakistan coast seems to have decreased by more than one-third. Over the same period, the regional oxygen minimum zone weakened, increasing the supply of oxygen to the sediments, leaving the expected imprint on a suite of redox-sensitive elements and reducing the preservation of organic matter.