Title: Dr' Julie BrighamGrette Professor, University of Massachusetts' PhD, University of Colorado 1985 M'S
1Dr. 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.
2Déjà vu a Paleoenvironmental Look at Sea Ice
Extent during Earlier Warm Periods
Julie Brigham-Grette and Zachary Lundeen
With unpublished model input from Bette
Otto-Bleisner (NCAR), Gifford Miller
(Colorado) And Jon Overpeck (Arizona)
3Where we are now less than 2 of geologic time
Hayes et al., 1998
4FactThere are no analogs for the future we face
- Must learn more from the Paleorecord Earth
under different forcings and mean states.
5Refined age for the earliest opening of the
Bering Strait at 5.32 Ma (Paleo3, 2002)
A. Gladenkov Oleinik Marincovich Barinov
6Ellesmere Island Meighen Island
Hvitland Beds 3.2 Ma
Bob Corell
- Marine sediments
- Arctica islandica
- 5 types of Pines
- Overlain by
- First evidence of Tundra
No Arctic Sea Ice even in Winter No Greenland Ice
Sheet
7Pliocene Sea level record
Skull Cliff, SW of Barrow
Northern 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
Wainwrightian
Fishcreekian
8Significant Northward Range extensions in marine
biota -- significantly warmer waters in Beringia
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 gt40 m 3.0 Ma
gt40 m
Maps Created by Bill Manley
9North Slope Alaska
Warm Pliocene Transgressions
2.4 Ma 2.6 Ma 3.0 Ma
Did the earliest glaciations occur when the
Arctic Ocean was ice free? (as proposed by
Hamilton for the Gunsight Mt. Glaciation)
103.0 My
Pliocene Vegetation Warmer/Wetter Pollen by
Robert Nelson, Colby College ____________ Offshore
warm too No seasonal Arctic sea ice during
interglacials
2.6 My
2.4 My
11Why Study the Last Interglacial
Generally Speaking Last time global climates
were significantly warmer than present A
possible analog for future warm climates
Concentration of Last Interglacial sites Europe
and the North Atlantic Alaska Few sites in
Siberian part of the Arctic
12Cuffey Marshall, 2000, Nature
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14During 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 max 5e
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
Winter sea ice today
Maps Created by Bill Manley
15Solar Radiation Changes at 70NAt top of
atmosphere
- 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).
Otto-Bliesner et al., in prep. Outgrowth of
recent PAGES-CAPE meeting
16Summer (JJA) surface air temperature anomalies
Data versus CCSM Model
Last Interglacial
4 to 8
2
4
5
6 to 8
2 to 3
6
CAPE Last Interglacial Working Group, in prep.
2
2 to 4
17CCSM Summer (August) Sea Ice Area ()
Present
130 ka
130 ka - Present
Otto-Bliesner et al., in prep.
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20Elemental and Isotopic Constraints on the
Late-Glacial/Holocene Paleoceanography of the
Chukchi SeaZach LundeenUniversity of
Massachusetts-Amherst
21Why 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
22Modern Circulation
23Chukchi Sea Bathymetry and Primary Currents
2414.5-16.5ka
10-12ka
-108m
-64m
-50m
Modified from Manly, W.F., 2002 Postglacial
Flooding of the Bering Land Bridge A Geospatial
Animation INSTAAR, University of Colorado, v1
8-9.5ka
-22m
-36m
-0m
25Global Sea Level Reconstruction
10-12ka Bering Strait sill depth breeched
Sea Level curve based on Lambeck et al, 2002
26Estimated Transgressive Ages at Core Sites
JPC10 10-12ka
JPC24 12.5-14ka
JPC28 14.5-16.5ka
Sea Level curve based on Lambeck et al, 2002
27Carbon 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
28- 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
Nitrogen Isotopes
29C3 land plants
C4 land plants
DIC
Atm. CO2
Marine phytoplankton
10
0
-10
-20
-30
Typical ?13C values
Average terrestrial OM from 12 Siberian rivers
and MacKenzie River - ?13C values -26 to -27
30Modern Sedimentary OM ?13C
Modified from Naidu et al., 2000
31C/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
32Core Sites
JPC28
JPC24
JPC10
33- 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 gt1 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.
34Core Sites
JPC28
JPC24
JPC10
35JPC 28
366700 14C yrs BP 7000 cal yrs BP
JPC28
JPC24
37JPC 28 Age Model a.k.a. The dreaded wiggle match
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.
Actual date
38- 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.
39Modern Sea Ice Maxima - March
Modern Sea Ice Minima - October
40Modern Surface Circulation Through Canadian Arctic
The Dyke et al., story
41Conditions 9-10Ka BP
42Speculation
- 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
43The 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
44Conclusions
- 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
45Thank you !