Dr. Julie Brigham-Grette Professor, University of Massachusetts. PhD, University of Colorado (1985)...
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Transcript of Dr. Julie Brigham-Grette Professor, University of Massachusetts. PhD, University of Colorado (1985)...
Dr. Julie Brigham-Grette Professor, University of Massachusetts. PhD, University of Colorado (1985) M.S., University of Colorado, (1980)
Research Interests: • late Cenozoic marine and non-marine stratigraphic problems in Arctic regions • paleogeography and sea level history of Alaska and the circum- Arctic coast • Arctic climate evolution • deglacial history of New England, and in the development of better chronostratigraphic methods combining a number of geochronological techniques.
Déjà vu: a Paleoenvironmental : a Paleoenvironmental Look at Sea Ice Extent duringLook at Sea Ice Extent during Earlier Warm PeriodsEarlier Warm Periods
Julie Brigham-Grette and Zachary LundeenJulie Brigham-Grette and Zachary Lundeen
With unpublished model input from Bette Otto-Bleisner (NCAR), Gifford Miller (Colorado)And Jon Overpeck (Arizona)
Where we are now – less than 2% of geologic time
INCREASING INSOLATION AT 65 N
INTERGLACIAL
THE INTERGLACIAL STATE OF THE CLIMATE SYSTEM
SENSIBLE HEATDRIVEN
Hayes et al., 1998
Fact:There are no analogs for the future we face
Must learn more from the Paleorecord = Earth under different forcings and mean states.
Refined age for the earliest opening of the Bering Strait at 5.32 Ma (Paleo3, 2002)
A. GladenkovOleinik
MarincovichBarinov
Ellesmere IslandEllesmere IslandMeighen IslandMeighen Island
Hvitland Beds~ 3.2 Ma
Marine sedimentsMarine sediments •Arctica islandica•5 types of Pines
Overlain by Overlain by
First evidence of TundraFirst evidence of Tundra
No Arctic Sea Ice even in Winter
No Greenland Ice Sheet
Bob Corell
Skull Cliff, SW of Barrow
Wainwrightian
Fishcreekian
Pliocene Sea level
recordNorthern Alaska
Gubik Formation
Sea Level Transgressions
Simpsonian 80 ka
Pelukian 125 ka
Wainwrightian 410 ka
Fishcreekian 2. 4 Ma
Bigbendian 2.6 Ma
Colvillian ~ 3.0 Ma
Maps Created by Bill Manley
Shoreline Elevations
MIS 5a 6-7 m
MIS 5e 8-10 m
MIS 11 22-23 m
~2.4 Ma ~33 m
~2.6 Ma >40 m
~3.0 Ma >40 m
Significant Northward Range extensions in marine biota -- significantly warmer waters in Beringia
Warm Pliocene
Transgressions
Did the earliest glaciations occur when the Arctic Ocean was ice free?(as proposed by Hamilton for the Gunsight Mt. Glaciation)
North Slope Alaska
~2.4 Ma
~2.6 Ma
~3.0 Ma
Pliocene Vegetatio
nWarmer/WetterPollen by Robert Nelson,
Colby College
____________
Offshore warm too
No seasonal Arctic sea ice
during interglacials
~3.0 My
~2.6 My
~2.4 My
Generally Speaking:• Last time global climates were significantly warmer than present• A possible analog for future warm climates
Why Study the Last Interglacial
Concentration of Last Interglacial sites• Europe and the North Atlantic• Alaska• Few sites in Siberian part of the Arctic
Cuffey & Marshall, 2000, Nature
Maps Created by Bill Manley
During 5e, winter sea ice limit ~800 km north of present, Bering Sea ice free year around; Arctic Ocean nearly ice
free some summers Brigham-Grette &
Hopkins, 1995 QR
During 5e, Treeline migration of ~600 km north ward; in many areas tundra eliminated from the arctic coast in NE Siberia Lozhkin and Anderson, 1995 QR
Winter sea ice today
Winter sea ice max 5e
Otto-Bliesner et al., in prep.Outgrowth of recent PAGES-CAPE meeting
*
• Holocene solar anomaly of 50 W/m2 exceeded from 133 to 125 ka.
• At 130 ka, maximum anomaly occurs in May (+70 W/m2) and minimum anomaly occurs in September (-50 W/m2).
Solar Radiation Changes at 70N
At top of atmosphere
+2 to +4 +2
Summer (JJA) surface air temperature anomalies
+6 CAPE Last Interglacial Working Group, in prep.
+6 to + 8
+4 to + 8
+2
+2 to +3
≥ +4
+5
Last Interglacial
Data versus CCSM Model
CCSM Summer (August) Sea Ice Area (%)
130 ka - Present
Present130 ka
Otto-Bliesner et al., in prep.
Elemental and Isotopic Constraints on the Late-Glacial/Holocene Paleoceanography of the Chukchi Sea
Zach LundeenUniversity of Massachusetts-Amherst
Why is Bering Strait area important?
•Bering Strait through-flow provides ~1/3 of fresh water flux to Arctic Basin-affects heat budget
•helps maintain a strong halocline that enhances sea ice formation and isolates warmer Atlantic derived water from exchanging heat with the atmosphere
•Affects sea ice export to Atlantic, with possible implications for global thermohaline circulation•Chukchi Sea is a significant carbon sink
today• surface water in summer is consistently undersaturated with CO2 due to biological drawdown and physical water mass changes that alter carbonate system equilibrium•Changes in land sea distribution following LGM
are likely to have affected the local climate by altering maritime influences
Modern CirculationWater Mass Salinity (psu) Temp
(Degrees C)Comments
Anadyr Water 32.7 - 33 -1.9 to 4 Nutrient rich
Alaskan Coastal
<31.9 f.p. to 12 Seasonal, nutrient poor
Bering shelf 31.9 - 32.7 f.p. to 7
Chukchi Sea Bathymetry and Primary Currents
Modified from Manly, W.F., 2002 Postglacial Flooding of the Bering Land Bridge:A Geospatial Animation: INSTAAR, University of Colorado, v1
-108m -64m -50m
-36m -22m -0m
14.5-16.5ka 10-12ka
8-9.5ka
10-12ka Bering Strait sill depth breeched
Global Sea Level Reconstruction
Sea Level curve based on Lambeck et al, 2002
JPC28 14.5-16.5ka
JPC24 12.5-14ka
JPC10 10-12ka
Estimated Transgressive Ages at Core Sites
Sea Level curve based on Lambeck et al, 2002
Carbon Isotopes in Organic Matter
Carbon isotopic compositions of organic matter are determined by :
• Source of carbon - atmospheric CO2, dissolved inorganic carbon (DIC)
•Fractionation during photosynthesis - dependant on pathway. C3 (-20‰) vs C4 (-7‰)
•Availability of carbon source - high concentrations lead to more fractionation, low concentrations lead to less fractionation
•Cell geometry (surface area) and growth rate- large, fast growing cells are generally less depleted in C-13 than small, slow growing cells
•Diagenetic alteration- selective loss of isotopically heavy constituents (proteins, carbohydrates) can alter residual OM composition. Incorporation of isotopically depleted bacterial biomass can also affect bulk properties
Nitrogen isotopic composition determined by:•Source of nitrogen- atmospheric, dissolved inorganic nitrogen (NO3, NH4, etc.), particulate organic nitrogen
•Trophic level- enrichment in N-15 occurs at each trophic level due to preferential excretion of N-15 depleted waste products
•Availability of nitrogen source- degree of nutrient utilization affects the ability to preferentially use N-14. High degree of utilization will result in relatively enriched 15N values
•Diagenetic Alteration- under highly productive waters denitrification can occur, preferentially releasing N-14. Selective degradation can also affect composition of residual OM
Aah, a cool pint of
Guinness!
Nitrogen IsotopesNitrogen Isotopes
Typical 13C values
10 0-10-20-30
Marine phytoplankton
C3 land plants C4 land plants
Atm. CO2
DIC
Average terrestrial OM from 12 Siberian rivers and MacKenzie River - 13C values = -26 to -27‰
Values observed today in study area
105 0-5-10
Marine phytoplanktonLand plants
Atm N2Dissolved NO3
Typical 15N values
Modified from Naidu et al., 2000
Modern Sedimentary
OM 13C
C/N Ratios•OC/N ratios of OM can be used do differentiate terrestrial sources from marine sources, or indicate degree of degradation
•Typical marine OM has C/N value ~ 6-7
•Typical terrestrial OM has C/N values from 20-400
•Marine OM C/N values typically increase with diagenetic alteration as nitrogen rich compounds are preferentially utilized
•Soil OM has lower C/N than parent materials due to adsorption of nitrogen compounds in soils
•Particulate OM in 12 Siberian rivers (highly degraded) had average C/N of ~11, dissolved OM C/N ~40
•Susceptible to misinterpretation in sediments with low organic content due to inorganic nitrogen (not significant in organic rich seds)
•Somewhat grain size dependant
JPC10
JPC28
JPC24
Core Sites
3.00
4.00
5.00
6.00
7.00
8.00
0 2000 4000 6000 8000 10000 12000 14000
Age (cal yrs BP)
del 1
5N
0.400.600.801.001.201.401.601.80
0 2000 4000 6000 8000 10000 12000 14000Age (cal yr BP)
%O
C
5.00
6.00
7.00
8.00
9.00
10.00
11.00
0 2000 4000 6000 8000 10000 12000 14000
Age (cal yrs BP)
OC
/N
-25.50
-24.50
-23.50
-22.50
-21.50
0 2000 4000 6000 8000 10000 12000 14000
Age (cal yrs BP)
del 1
3C
•Increased productivity leads to denitrification in sediments leading to higher ) 15N values
•8500 ka event shows low TOC, depleted (terrestrial) 15N values, low (marine) C/N values, 13C values relatively unchanged
•11ka- abrupt increase in TOC from ~0.65% to 0.9%, and >1‰ increase in 15N coincident with transgression of sill depth at Bering Strait
•After ~8.5ka, sharp increase in TOC, %N, 15N values, and 13C values.
0.05
0.1
0.15
0.2
0.25
0 2000 4000 6000 8000 10000 12000 14000
%N
JPC10
JPC28
JPC24
Core Sites
0.600.801.001.201.401.601.802.00
0 100 200 300 400 500 600 700
Depth in Core (cm)
%O
C
-25.0
-24.5
-24.0
-23.5
-23.0
-22.5
-22.0
-21.5
-21.0
0 100 200 300 400 500 600 700
Depth in Core (cm)
del
13C
3
4
5
6
7
8
9
0 100 200 300 400 500 600 700
Depth in Core (cm)del 15N
6.0
6.5
7.0
7.5
8.0
8.5
9.0
9.5
0 100 200 300 400 500 600 700
OC
/N
y = 0.1175x + 0.0242R2 = 0.9916
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.0 0.5 1.0 1.5 2.0
%OC
%N
0.05
0.10
0.15
0.20
0.25
0 100 200 300 400 500 600 700
Depth
%N
JPC 28
1.25
1.5
1.75
2
2.25
0 1 2 3 4 5 6 7
depth (m)
dens
ity (g
/cc)
-25.0
-24.5
-24.0
-23.5
-23.0
-22.5
-22.0
-21.5
-21.0
0 100 200 300 400 500 600 700
Depth in Core (cm)
del
13C
-25.50
-24.50
-23.50
-22.50
-21.50
0 2000 4000 6000 8000 10000 12000 14000
Age (cal yrs BP)
del 1
3C
6700 14C yrs BP= ~7000 cal yrs BP
Assumed to be synchronous
JPC28
JPC24
-25.5
-25.0
-24.5
-24.0
-23.5
-23.0
-22.5
-22.0
-21.5
-21.0
0 2000 4000 6000 8000 10000 12000 14000 16000age (cal yr BP)
del 1
3C
jpc28
jpc24
JPC 28 Age Modela.k.a. “The dreaded wiggle match”
Actual date
Note: The two data sets were analyzed in different labs, JPC24 was done at UMASS, JPC 28 was analyzed at UKentucky. All samples from both data sets were treated and packed into capsules at UMASS.
7.00
7.50
8.00
8.50
9.00
9.50
0 2000 4000 6000 8000 10000 12000 14000 16000
OC
/N
0.600
0.900
1.200
1.500
1.800
0 2000 4000 6000 8000 10000 12000 14000 16000
Age (cal yr BP)
%O
C
-25.0
-24.5
-24.0
-23.5
-23.0
-22.5
-22.0
-21.5
0 2000 4000 6000 8000 10000 12000 14000 16000
cal age BP
del 1
3C
3.0
4.0
5.0
6.0
7.0
8.0
9.0
0 2000 4000 6000 8000 10000 12000 14000 16000
cal age bp
del 1
5N
•~8500ka abrupt increase in TOC, C/N, 15N, and 13C
•N isotopic shift indicative of increased relative marine OM input, higher degree of nutrient utilization, and/or denitrification in sediments- consistent with sharp increase in OM delivery to sediments
•Shift in C isotopes is indicative of higher productivity (biological drawdown of DIC), with possible additional influence of temperature effects on pCO2 of sea water
•Steady increase of 13C values from 7ka to present is likely a diagenetic signal- more selective degradation due to increased supply
•C/N shift at ~8500 is also likely to be an indicator of more selective degradation of OM due to increased supply.
Modern Sea Ice Maxima - March Modern Sea Ice Minima - October
The Dyke et al., story…
Modern Surface Circulation Through Canadian Arctic
Conditions 9-10Ka BP
Speculation…
Alternative ways to cut off the nutrient source:
•Remove the transport pathway- freshwater lens in Arctic reverses the sea level gradient and slows or halts the northward flow through the Bering Strait?-mollusk evidence against idea
•Remove the nutrients from the transported water mass- upwelling absent off Gulf of Anadyr prior to 8-9Ka?- radiolarian assemblages may support idea
The Early Holocene Reorganization•Increased sea ice in the Canadian Arctic after 8500 yrs as evidenced by lack of bowhead whale remains
•Increased salinity in the Canadian Arctic after 9000 due to decreased meltwater
•Shift in path of Trans Polar Drift ~8500 yrs BP evidenced by drift wood distribution
•Foraminiferal biozone change at ~8500 yr BP associated with changes in Atlantic incursion into Arctic Basin
Conclusions• Arctic Sea ice became perennial about 2.4 Ma ago.
Permafrost more widespread. • Sea Ice extent likely impacted Pliocene glacial ice
extent• Warmer waters have repeatedly entered the Arctic
Basin, esp. during warmer interglacials. • Winter Sea Ice limit was likely 800 km north of today
about 125 ka• During the Last Interglacial, some summers may
have been without sea ice (Atlantic layer water shallower)
• Sea ice was less than present during most of the early Holocene across the Arctic.
• Significant changes in Arctic Sea Ice distribution, water mass characteristics and circulation have been documented ~8500 ka suggesting a possible driving mechanism or a common response to a driving mechanism
• Diatom studies or other sea ice indicators may help develop a more definite interpretation of the data
Thank you !