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With unpublished model input from Bette Otto-Bleisner (NCAR), Gifford Miller (Colorado)And Jon Overpeck (Arizona)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 !