Proxy Calibration: An Example

1
Proxy Calibration An Example

• 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

2
Emiliania huxleyi Blooms

• 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
3
Emiliania huxleyi Makes Alkenones
4
UK37 Varies with Temperature

• Alkenone unsaturation global calibration
• UK37 determined in core top sediment samples
• SST from from Levitus ocean atlas
• Figure from Muller et al. (1998)

5
Global UK37 SST Correlation
6
Laboratory UK37 Calibrations
7
Ecology Potentially Affects UK37

• 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?N15?S) in
  the Pacific (175?W) fall near the lower limit or
  even below the annual range in SST (Ohkouchi et
  al., 1999)

8
Physiology Potentially Affects UK37
9
Global UK37 SST Correlation
10
Study Site Station ALOHA
11
Methods

• Alkenone export
• Sediment trap particles
• Determine UK37 of alkenone export flux

12
Methods

• Alkenone standing stock
• Large volume in situ particle collection
• Determine UK37 of alkenone in suspended
  particulate matter
• Compare UK37 and in situ temperature

13
Methods

• Determine alkenone production rate
• In situ 13C labeling experiments

14
Alkenone Production Rate

• Alkenone production rate (modified from Hama et
  al., 1993)
• ais is alkenone 13C atomic (C372 or C373) at
  the end of the incubation,
• ans is alkenone 13C atomic of alkenone (C372
  or C373) 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

15
In Situ Array

• Water collected from various depths
• Trace amount of H13CO3- added
• Array deployed for 24 hours
• Samples filtered and alkenone d13C measured
• 13C uptake rate calculated

16
Sample Collection

• CTD
• Conductivity
• Temperature
• Depth
• Fluorometer
• Chlorophyll a
• Oxygen sensor
• Sample bottles

17
Add H13CO3- (d13CDIC 190) bag bottles
Haul bagged bottles to rail and attached them to
line
18
Deploy bagged bottles
19
Deploy floats, spar buoy pray it all returns
20
Results July 2001

• C372 1 - 4 ng L-1
• C372 production lt0.1 1.2 ng L-1 d-1
• Maximum in excess DO maximum
• C372 production lowest in chl. maximum
• Depth of C372 and production maximum same
• UK37 T
• lt in situ in excess DO
• gt in situ in chl. maximum

21
Results February 2003

• C372 2 - 12 ng L-1
• Feb 03 gtgt Jul 01
• C372 production lt0.1 0.9 ng L-1 d-1
• Maximum in excess DO maximum
• Feb 03 lt Jul 01
• C372 production lowest in chl. maximum
• Depth of C372 and production maximum same
• UK37 T
• gt in situ in excess DO
• gtgt in situ in chl. maximum

22
Results February 2003

• Water from 120 m, incubated at 100, 80 and 40 m
• C372 increase
• 2.5-fold 80 m
• 4.7-fold 40 m
• C372 production increase
• 3.8-fold 80 m
• 5.0-fold 40 m
• UK37 T unaffected
• Growth light-limited in chl. maximum

23
ALOHA SST Time Series
24
Conclusions UK37 at ALOHA

• 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 UK37
• 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

25
Guaymas Basin 2004-2005
26
Guaymas Basin 2004-2005
Comparison of AVHRR SST for 1996-97 with
difference between UK37 temperature measured in
sediment trap particles and AVHRR SST (data from
Goni et al., 2001)
27
Historical Records

• 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

28
Sources of Historical Data

• 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

29
Problems with Historical Data

• 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

30
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

31
Stable Isotope Analyses

• The vapor pressure of H216O gt 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
• Water vapor becomes increasingly depleted in
  H218O
• 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

32
Physical Chemical Characteristics

• 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

33
Air Bubbles in Ice

• 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

34
Dissolved and Particulate Matter

• Variations of dissolved and particulate matter
  can be used as proxy paleoclimatic indicators
• Calcium
• Aluminum
• Silicon
• Iron
• Dust
• Certain atmospheric aerosols

35
Dating Ice Cores

• 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
• Radioisotope dating (210Pb, 32Si, 39Ar, 14C) have
  been used with varying degrees of success
• Characteristic layers provide valuable
  chronostratigraphic markers
• Major explosive volcanic eruptions emit sulfur
  increase acidity of ice