Selected Presentation from the INSTAAR Monday Noon Seminar Series.

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1 Selected Presentation from the INSTAAR Monday Noon Seminar Series. Institute of Arctic and Alpine Research, University of Colorado at Boulder. This seminar presentation has been posted to the internet to foster communication with the science community and the public. Most of the INSTAAR presentations were originally given in PowerPoint format; they were converted to Adobe PDF for posting. You may need to install the free Adobe Acrobat Reader to view these files. These presentations are "works in progress". They are not peer reviewed. They should not be referenced for any kind of publication. Contact the author for proper references and additional information before any use, even for unpublished works such as your own presentations. LICENSING AGREEMENT. Free use of these presentations is limited to a nonprofit educational or private non-commercial context and requires that you contact the author, give credit to the author, and display the copyright notice. All rights to reproduce these presentations are retained by the copyright owner. Images remain the property of the copyright holder. By accessing these presentations, you are consenting to our licensing agreement. 22 Sep Tom Marchitto, INSTAAR. "Atlantic-Pacific climate teleconnections at millennial time scales." Seminar given at INSTAAR, University of Colorado. Copyright 2003 Tom Marchitto. All Rights Reserved. Marchitto presentation (3.1 Mb PDF).

2 Selected Presentation from the INSTAAR Monday Noon Seminar Series. Institute of Arctic and Alpine Research, University of Colorado at Boulder Sep Tom Marchitto, INSTAAR. "Atlantic-Pacific climate teleconnections at millennial time scales." Seminar given at INSTAAR, University of Colorado. Copyright 2003 Tom Marchitto. All Rights Reserved. Marchitto presentation (3.1 Mb PDF). Abstract The climate of the Northern Hemisphere during the last glaciation was dominated by so-called Dansgaard/Oeschger cycles, which are rapid, large magnitude climate swings first identified in Greenland ice cores. These cycles have recently been found in a number of tropical and subtropical records, indicating the existence of long-range climate teleconnections that are poorly understood. Organic matter concentrations in a sediment core from the oxygen minimum zone (OMZ) off southern Baja California (705 m water depth) vary in concert with Dansgaard/Oeschger oscillations. A measure of sediment color (the third principal component of the diffuse spectral reflectance) displays a particularly striking similarity to Greenland ice core temperature records over the past 50 kyr. High organic matter concentrations during interstadials and during the Holocene may have been caused by increased productivity and/or increased preservation due to reduced OMZ ventilation. Changes in ventilation could have been caused by competition between warm, salty, low-oxygen (tropical) intermediate waters and cool, fresh, high-oxygen (North Pacific) intermediate waters. Temperatures derived from benthic foraminiferal Mg/Ca are inconsistent with this ventilation scenario, however. Rather, we believe that productivity has been the dominant control on organic matter accumulation and northeastern Pacific OMZ strength. Modern productivity in this region is controlled by ENSO dynamics, and we suggest that a North Atlantic-Asian monsoon-enso linkage might explain the observed hemispheric distribution of Dansgaard/Oeschger variability.

3 Atlantic-Pacific climate teleconnections at millennial time scales Tom Marchitto University of Colorado, Boulder Marta Vicarelli École Normale Supérieure, Paris Joe Ortiz Kent State University Jose Carriquiry Universidad Autónoma de Baja California Alberto Sanchez Universidad Autónoma de Baja California Walt Dean USGS, Denver Yan Zheng Queens College, CUNY Lex van Geen Lamont-Doherty Earth Observatory

4 Outline Global distribution of millennial-scale climate variability during last glacial period Eastern Pacific (Baja California) oxygen minimum zone intensity: Ventilation or productivity? Linking things together: North Atlantic, Asian monsoons, and ENSO

5 El Niño modern climate teleconnections La Niña El Niño (NOAA/IRI) Strong easterlies Strong eastern upwelling (cold SSTs) Heavy rainfall in western warm pool Weak easterlies Weak eastern upwelling (warm SSTs) Eastward shift in rainfall

6 Greenland (GISP2) air temperatures Grootes and Stuiver (1997)

7 Magnitude and rapidity of warmings from d 15 N Bølling (IS1) warming 9 ±3ºC over several decades (Severinghaus and Brook, 1999) IS19 warming 16 ±2ºC over ~160 yr (Lang et al., 1999)

8 Dansgaard-Oeschger signal in North Atlantic Bond et al. (1993, 1999) warm % N. pachy (s.) 54ºN cold H1 H2 H3 H4 H5 H6 ~5ºC SST oscillations Massive iceberg discharges (Heinrich events) every several stadials 50ºN H1 H2 H3 H4 H5 H6

9 Meridional overturning circulation as forcing (e.g. Schmittner et al., 2002, after Broecker et al., 1985) cold deep warm surface Warm interstadial state: MOC strong, ice sheet growing increased calving and southern marginal melting reduced sea surface salinities MOC collapse Cold stadial state: reduced calving increased sea surface salinities MOC resumption

10 Some notable D-O oscillations outside North Atlantic Santa Barbara Basin Cariaco Basin Hulu Cave Arabian Sea Bay of Bengal Indonesia

11 Cariaco Basin (Venezuela) Peterson et al. (2000) Stadials: Lighter in color Less Ti, Fe, calcite accumulation Less runoff, less productive reflectance ITCZ shifted south

12 Arabian Sea Schulz et al. (1998) Stadials: Less organic carbon Lighter d 15 N (Altabet et al., 2002) Less productivity Less upwelling Weaker summer monsoon organic carbon

13 Bay of Bengal Kudrass et al. (2001) Stadials: Heavier planktonic d 18 O (Mg/Ca ~same) Saltier sea surface Less runoff Weaker summer monsoon surface salinity (inverted) planktonic d 18 O

14 Hulu Cave (Nanjing, China) Wang et al. (2001) Stadials: Heavier d 18 O More winter-like precipitation stalagmite d 18 O Stronger winter monsoon and/or Weaker summer monsoon

15 Indonesian warm pool Stott et al. (2002) Stadials: Heavier planktonic d 18 O (Mg/Ca ~same) Saltier sea surface Less precipitation Shift of warm pool atmospheric convection center fresh planktonic Dd 18 O fresh salty El Niño-like mean state salty

16 Santa Barbara Basin Behl & Kennett (1996) Stadials: Bioturbated sediments Increased bottom water O 2 bioturbation Stronger North Pacific Intermediate Water ventilation

17 Byrd, West Antarctica Blunier and Brook (2001) Stadials: Enriched ice d 18 O Warm air Heat left in Southern Hemisphere when NADW slows ( bipolar see-saw )

18 D-O stadial pattern summary more NPIW(?) dry cold weak winds dry summers/ wet winters dry dry warm warm

19 California margin ventilation Intense oxygen minimum zone (OMZ) at intermediate depths North Pacific Intermediate Water: cool, fresh, high-o 2 Tropical intermediate waters: warm, salty, low-o 2

20 Foraminiferal d 18 O as a temperature/salinity proxy calcite d 18 O decreases with temperature seawater d 18 O increases with salinity Lynch-Stieglitz et al. (1999) high (heavy) d 18 O foram = cold, salty, large global ice volume low (light) d 18 O foram = warm, fresh, small global ice volume

21 Greenland SBB Santa Barbara Basin benthic d 18 O Hendy & Kennett (2002) Antarctica benthic planktonic Bottom waters (sill depth 450 m) cooler (or saltier) during high-o 2 stadials Interstadial bottom warmings seem to precede surface warming and O 2 decrease

22 Santa Barbara Basin ventilation hypothesis Hendy & Kennett (2002) Stadials well-ventilated by cool, fresh, high-o 2 North Pacific Intermediate Water Tropical undercurrent strengthens ~140 yr prior to interstadials (but tropical waters not yet low-o 2 ) Interstadials bathed by warm, salty, low-o 2 tropical waters Leaves oxygenation of tropical OMZ unexplained

23 collected m water depth open margin O 2 = 2 mmol/kg coarsely laminated surface sediments Baja California core GC31/PC08

24 Diffuse spectral reflectance (DSR) stratigraphy Ortiz et al. (submitted) 1-cm measurements (at sea) using hand-held spectrophotometer First derivative ( R/ l) defines spectral shape of each sample 3-component R-mode factor analysis accounts for >93% of variance Factor 1 = 60% ~CaCO 3 Factor 2 = 23% ~g-fe 2 O 3 (?) Factor 3 = 10% ~organic carbon

25 Organic carbon variability (705 m) stadials lighter in color (low F3 score) and lower in organic C F3 may record initial OC or O 2 through redox influence on sediment color

26 Radiocarbon age model near-linear sedimentation no age reversals 3 rd -order polynomial for top 5 m Radiocarbon ages consistent with calendar age (GISP2) picks

27 Hypothesis If organic matter content (and OMZ strength) were mainly controlled by North Pacific ventilation, then intermediate waters should have been cooler during low-organic, high-oxygen periods (stadials, YD, LGM) Such cooling should be recorded by the Mg content of the benthic foraminifer Uvigerina peregrina Methods ~20-60 U. peregrina (>250 mm) per sample Full reductive and oxidative trace metal cleaning after Boyle Measurement by ICP-AES with analytical precision of ±0.018 mmol/mol (1s) Pooled standard deviation of replicate samples was ±0.042 mmol/mol

28 Foraminiferal Mg/Ca temperature proxy Mashiotta et al. (1999) Mg/Ca increases exponentially with temperature Expected from thermodynamics, but likely biological too Better constrained for planktonics than for benthics

29 Benthic (U. peregrina) Mg/Ca results Bølling/Allerød marginally warmer then pre-bølling (P=0.02) Younger Dryas even warmer than B/A and Holocene (P=0.0001) Coldest during late Holocene (post-4.5 kyr BP) Several abrupt changes within Holocene Inconsistent with ventilation control on OMZ strength

30 Temperature calibration Uvigerina calibration poorly defined (multiple species problem?) 15% per ºC temperature sensitivity after Martin et al. (2002) Late Holocene 5.7 ±0.6ºC Younger Dryas 7.2 ±0.5ºC Abrupt shifts order 1ºC

31 Benthic stable isotopes Low d 13 C during high-organic interstadials No obvious D-O variability in d 18 O

32 Seawater d 18 O Virtually all of Uvigerina d 18 O signal due to seawater d 18 O changes Total magnitude exceeds ice volume by at least 0.5 Coolings accompanied by freshening (North Pacific-like waters)

33 Productivity proxy benthic foram abundance (accumulation) dropped sharply during stadials not a preservation signal suggests reduced primary productivity during high-o 2 intervals

34 El Niño impact at Baja (Takesue et al., in press) SST anomalies December 1997 Thermocline and nutricline deepen Upwelling waters warmer and poorer in nutrients Productivity reduced El Niño surface Cd, P coastal upwelling index

35 Oxygen minimum zone ENSO hypothesis Stadials were characterized by an El Niño-like mean state, resulting in reduced productivity (due to deeper nutricline) and hence a weaker OMZ. North Pacific ventilation was of minor importance. Consistent paleoclimate records Drier western Pacific warm pool (Stott et al., 2002) Reduced east-west tropical Pacific SST gradient (Koutavas et al., 2002) Southward penetration of ITCZ over South America (Peterson et al., 2000) Weaker Indian summer monsoon (Schulz et al., 1998; Kudrass et al., 2001) Stronger east Asian winter monsoon (Wang et al., 2001)

36 D-O ENSO driven from North Atlantic? wind anomalies A snow cover anomalies North Atlantic Asia GCM: YD cold North Atlantic SSTs and Scandinavian Ice Sheet more Tibetan snow weaker summer monsoon (Overpeck et al., 1996) Asia tropical Pacific Strong east Asian winter monsoon followed by weak Indian summer monsoon and strong Australian winter monsoon El Niño (Chen and Wu, 2000)

37 Conclusions Intermediate water temperatures across the Bølling/Allerød-Younger Dryas oscillation are inconsistent with a North Pacific ventilation control on eastern Pacific OMZ strength Organic matter accumulation and OMZ strength appear to have been dominated by productivity changes, possibly due to ENSO-like dynamics Unanswered questions (future work) Were stadials really characterized by El Niño-like conditions? Do global climate models support a North Atlantic-monsoon-ENSO chain of forcing on millennial time scales? Could millennial scale variability have originated in the ENSO system?