Transcript Document 7461584

Proxy Calibration: An Example
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Emiliania huxleyi is one
of 5000 or so species of
phytoplankton
Most abundant
coccolithophore on a
global basis, and is
extremely widespread
 Occurs in all except
the polar oceans
Produces unique
compounds
 C37-C39 di-, tri- and
tetraunsaturated
methyl and ethyl
ketones
Alkenones as biomarkers
• Long-chain (C37-C39) di-, tri- and tetraunsaturated methyl and ethyl ketones
(alkenones) found in oceanic sediments
Emiliania huxleyi Blooms
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E. huxleyi can occur in
massive blooms
 100,000 km2
 During blooms E.
huxleyi cell
numbers usually
outnumber those of
all other species
combined
 Frequently they
account for 80
or 90% of the
total number of
phytoplankton
SeaWiFS satellite image of bloom off Newfoundland
in the western Atlantic on 21 July 1999
Emiliania huxleyi Makes Alkenones
UK’37 Varies with Temperature
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Alkenone unsaturation
global calibration
 UK’37 determined in
core top sediment
samples
 SST from from
Levitus ocean atlas
 Figure from Muller
et al. (1998)
Global UK’37 SST Correlation
Laboratory UK’37 Calibrations
Ecology Potentially Affects UK’37
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Highest alkenone biomass was found within the
chlorophyll maximum in the western
Mediterranean (Bentaleb et al., 1999)
Alkenone export flux in sediment traps (1 km
deep) in temperate NE Pacific traceable by its
UK'37 signature to chlorophyll maximum in
overlying waters (Prahl et al., 1993)
Temperature estimates from UK'37 in surface
sediments along a N-S transect (~50N–15S) in
the Pacific (~175W) fall near the lower limit or
even below the annual range in SST (Ohkouchi et
al., 1999)
Physiology Potentially Affects UK’37
Global UK’37 SST Correlation
Study Site: Station ALOHA
HOT 124: 19-23 Mar 2001
KOK 011: 16-23 Jul 2001
HOT 131: 21-26 Oct 2001
KOK 303: 17-22 Feb 2003
HOT 1: 29 Oct – 3 Nov 1988
HOT 155: 20-24 Jan 2004
Methods
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Alkenone export
 Sediment trap
particles
 Determine UK’37 of
alkenone export
flux
Methods
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Alkenone standing stock
 Large volume in situ
particle collection
K’
 Determine U 37 of
alkenone in suspended
particulate matter
• Compare UK’37 and
in situ temperature
Methods
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Determine alkenone
production rate
 In situ 13C labeling
experiments
Alkenone Production Rate
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Alkenone production rate (modified from Hama
et al., 1993)
Production
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ais  ans  alkenone (t )
Rate 
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aic  ans 
t
ais is alkenone 13C atomic % (C37:2 or C37:3) at the end of
the incubation,
ans is alkenone 13C atomic % of alkenone (C37:2 or C37:3)
in the natural (nonincubated) sample,
aic is CO2(aq) 13C atomic % in the incubation bottle,
alkenone (t) is the alkenone concentration at the end
of the incubation
t is the length of the incubation
In Situ Array
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Water collected from
various depths
Trace amount of
H13CO3- added
Array deployed for 24
hours
Samples filtered and
alkenone d13C
measured
13C uptake rate
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calculated
Sample Collection
CTD
 Conductivity
 Temperature
 Depth
 Fluorometer
 Chlorophyll a
 Oxygen sensor
 Sample bottles
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Add H13CO3(d13CDIC = +190‰)
& bag bottles
Haul bagged bottles to rail
and attached them to line
Deploy bagged bottles
Deploy floats, spar buoy
& pray it all returns
Results – July 2001
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[C37:2] ~1 - 4 ng L-1
C37:2 production <0.1
– 1.2 ng L-1 d-1
 Maximum in
excess DO
maximum
[C37:2] & production
lowest in chl.
maximum
Depth of [C37:2] and
production maximum
same
UK’37 T
 < in situ in
excess DO
 > in situ in chl.
maximum
Results – February 2003
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[C37:2] ~2 - 12 ng L-1
 Feb 03 >> Jul 01
C37:2 production <0.1
– 0.9 ng L-1 d-1
 Maximum in
excess DO
maximum
 Feb 03 < Jul 01
[C37:2] & production
lowest in chl.
maximum
Depth of [C37:2] and
production
maximum same
UK’37 T
 > in situ in
excess DO
 >> in situ in chl.
maximum
~1ºC
~2ºC
Results – February 2003
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Water from 120
m, incubated at
100, 80 and 40 m
[C37:2] increase
 2.5-fold 80 m
 4.7-fold 40 m
C37:2 production
increase
 3.8-fold 80 m
 5.0-fold 40 m
UK’37 T unaffected
Growth lightlimited in chl.
maximum
ALOHA SST Time Series
Conclusions: UK’37 at ALOHA
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Maximum alkenone production was found during all seasons in or
just below the surface mixed layer
Minimum alkenone standing stock and production were found in
deep chlorophyll maximum
 Alkenone-producer growth light-limited
 Expect minimal export flux to sediments
Non-thermal physiological processes affect UK’37
 Nutrient depletion can lead to underestimation of actual
growth temperature
 Light limitation leads to overestimation of actual growth
temperature
Measurements of standing stock alone do not allow conclusive
interpretation of production and export
Interstrain (or species) differences in alkenone biosynthesis
Guaymas Basin 2004-2005
Guaymas Basin 2004-2005
Comparison of AVHRR SST for 1996-97 with difference between UK’37
temperature measured in sediment trap particles and AVHRR SST (data from
Goni et al., 2001)
Historical Records
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Historical proxy data grouped into three major
categories
 Observations of weather phenomena
 The frequency and timing of frosts or the
occurrence of snowfall
 Records of weather-dependent natural or
environmental phenomena (parameteorological)
 Droughts and floods
 Phenological records of weather-dependent
biological phenomena
 The flowering of trees or the migration of
birds
Sources of Historical Data
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Sources of historical climate information
include
 Ancient inscriptions
 Annals and chronicles
 Government records
 Estate records
 Maritime and commercial records
 Diaries and correspondence
 Scientific or quasi-scientific writings
 Early instrumental records
Problems with Historical Data
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Accounts can be subjective
 How severe is a severe frost?
Reliability of the account
 Did author have first-hand evidence of event?
Is the account accurate and representative?
 What is the duration and extent of the event?
The data must be calibrated against recent
observations and instrumental data
 This might be achieved by construction of
indices (e.g. the number of reports of frost
per winter) which can be statistically related
to analogous information derived from
instrumental records
Glaciological – Ice Cores
Environmental conditions recorded as snow
and ice accumulates on ice caps and sheets
 Paleoclimate information is obtained from
ice cores by three main approaches
 Stable isotopes of water
 Dissolved and particulate matter in the
firn and ice
 Physical characteristics of the firn and
ice, and of air bubbles trapped in the ice
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Stable Isotope Analyses
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The vapor pressure of H216O > H218O
Evaporation of water results in vapor with less 18O than
the initial water
 The remaining water is enriched in 18O
During condensation, the lower vapor pressure of the
H218O enriches water in 18O
During pole ward transportation of water vapor, isotope
fractionation causes preferential removal of 18O
18
 Water vapor becomes increasingly depleted in H2 O
Because condensation is the result of cooling, the
greater the fall in temperature, the lower the heavy
isotope concentration
 Isotope concentration in the condensate (water, snow,
ice) can thus be considered as a function of the
temperature of condensation
Physical & Chemical Characteristics
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Occurrence of melt features in the upper layers
of ice cores provide climatic information
 Horizontal ice lenses and vertical ice glands
result from the refreezing of percolating
water
 Identified by their deficiency in air bubbles
 Relative frequency of melt interpreted as an
index of maximum summer temperatures or of
summer warmth in general
Other physical features of ices cores include
 Variations in crystal size
 Air bubble fabric
 Crystallographic axis orientation
Air Bubbles in Ice
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The atmospheric gas is trapped as air pores are closed
off during the transition of firn to ice
Considerable research has been devoted to the analysis
of carbon dioxide concentrations of air bubbles trapped
in ice cores
Dissolved and Particulate Matter
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Variations of dissolved and particulate
matter can be used as proxy paleoclimatic
indicators
 Calcium
 Aluminum
 Silicon
 Iron
 Dust
 Certain atmospheric aerosols
Dating Ice Cores
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Many different approaches used
 One of the biggest problems ice core studies is
determining age-depth relationship
 Accurate time scales for only last 10,000 years
Age-depth relationship highly exponential and ice flow
models needed to determine ages of deepest ice cores
Absolute and relative dating techniques
210Pb, 32Si, 39Ar, 14C) have been
 Radioisotope dating (
used with varying degrees of success
 Characteristic layers provide valuable
chronostratigraphic markers
 Major explosive volcanic eruptions emit sulfur;
increase acidity of ice