J. Nannoplankton Res. 26 (1), 2004, pp.1-12 © 2004 International Nannoplankton Association
ISSN 1210-8049 Printed by Cambridge University Press, UK

1

Coccolith size increase of Calcidiscus leptoporus offshore
Morocco during the Last Glacial Maximum: an expression ofenhanced glacial productivity?
Jorijntje Henderiks
Geological Institute, ETH-Z, Sonneggstrasse 5, CH-8092 Zürich, Switzerland. Present address: Inst. för Geologi och Geokemi, Stockholm
Universitet, S-106 91 Stockholm, Sweden; jorijntje.henderiks@geo.su.se

Sabrina Renaud
Geological Institute, ETH-Z, Sonneggstrasse 5, CH-8092 Zürich, Switzerland. Present address: S.R. Lab. Paléoenvironnements et Paléobiosphère,
UMR 5125 CNRS UCB Lyon I, F-69622 Villeurbanne, France

Abstract In recent years, the morphological variability of the coccolithophore species Calcidiscus leptoporus
has been studied from a global set of Holocene sediment samples and along seasonal variations in both plankton andsediment trap studies. These studies show inverse morphological trends with temperature. A direct application ofmorphological changes in fossil assemblages to reconstruct palaeoenvironmental conditions has remained limited,
although the seasonal investigations have offered additional insight in other ecological factors than temperature controlling the dynamics and distribution of C. leptoporus, such as nutrient availability and hydrographic conditions. In
this pilot study, we explore the possible causes of glacial-interglacial variability in its coccolith morphology in the
Canary Basin, by comparing our observations to the seasonal variations reported in the literature.
Size-measurements of C. leptoporus coccoliths in Holocene sediments from the NE Atlantic show smallest mean
size at low temperatures. In contrast, mean C. leptoporus coccolith-sizes in sediment samples corresponding to theLast Glacial Maximum (LGM) were significantly larger than their Holocene counterparts in the Canary Islands
region (NE Atlantic). We argue that this may be an expression of a change in productivity during the LGM, in favourof the production of C. leptoporus with large (>8µm) coccoliths.
Seasonal plankton samples off Bermuda (North Atlantic) revealed that during the nutrient-rich winter season the
production of large coccoliths was highest, whereas coccolith size was significantly decreased during summer. Veryrecently, similar observations in sediment traps from the NE Atlantic have been reported, with the largest C. leptoporus coccoliths encountered during spring blooms, under elevated nutrient conditions and lowered sea-surface temperatures.
During the LGM, coastal upwelling was generally enhanced offshore Morocco due to the increased strength of the
trade winds. Consequently, it is proposed that overall increased yearly nutrient input, together with cooler glacial
sea-surface waters, resulted in the dominant production of large ‘winter/bloom’-type coccoliths of C. leptoporus,
especially in the regions near the coastal upwelling zone.

Keywords Coccolith morphology, Calcidiscus leptoporus, glacial-interglacial variability, Last Glacial
Maximum, Atlantic, Canary Basin

1. Introduction
In few cases have coccolith assemblage studies of surface
sediments, and their relative changes down-core, beenused to infer temperature conditions and circulation patterns (e.g. Roth & Coulbourn, 1982; Okada & Wells,
1997; Wells & Okada, 1997; Takahashi & Okada, 2000),or productivity fluctuations (Molfino & McIntyre, 1990;
Beaufort et al., 1997, 2001). However, the process of
species-selective dissolution limits studies focusing on
coccolith assemblages alone. Carbonate dissolution takes
place both during settling of coccoliths out of the photic
zone and progressively within the sediments. To avoid
this potential bias, several studies have focused on themorphological variability (mainly size) of a single, or agroup, of species that are abundant in sediment samples

and are regarded as dissolution-resistant. Such studies
have revealed great morphological variability, which
could be related to specific environmental parameters andmay be the result of either genetic variability or ecophenotypy (e.g. Baumann, 1990, 1993; Young & Westbroek,
1991; Bollmann, 1997; Knappertsbusch et al., 1997).
Very recently, a new palaeotemperature proxy has beendeveloped, based on the morphology of the coccolithophore genus Gephyrocapsa (Bollmann et al., 2002).
Its application was validated off NW Africa, successfullyreconstructing sea-surface temperatures during the Last
Glacial Maximum (LGM; Henderiks & Bollmann, in
review).
Calcidiscus leptoporus (Murray & Blackman, 1898)
Loeblich & Tappan, 1978 is a cosmopolitan species, today

2

Henderiks & Renaud

ranging from equatorial to polar waters (McIntyre & Bé,
1967; Geitzenauer et al., 1977). Its fossil record dates
back to the Early Miocene (Young, 1998). Although C.
leptoporus never reaches high abundances in surfacewaters, it can dominate coccolith assemblages in sediments due to its resistance to dissolution (McIntyre &McIntyre, 1970). It is therefore regarded as a promising
species for palaeoceanographic reconstructions.
C. leptoporus has been shown to have a wide morphological variability in a global set of Holocene sediment
samples (Knappertsbusch et al., 1997), in sediment trap
time-series (Baumann & Sprengel, 2000; Renaud et al.,2002), and through seasonal variations in plankton samples (Renaud & Klaas, 2001). These studies show inverse
morphological trends with temperature. Knappertsbusch
et al. (1997) identified three morphotypes of C. leptoporus (‘small’ - coccolith diameter ≤5µm, ‘intermediate’- 5-8µm and ‘large’ - ≥8µm) within the living plankton,
which can be found down to Holocene sediments in various mixtures. They found that the relative frequency oflarge coccoliths (≥8µm) within Holocene surface sediments is positively correlated to mean annual sea-surface
temperature, with the largest coccoliths in tropical regions(Knappertsbusch et al., 1997). However, in seasonal samples, the individual responses of the three different C. leptoporus morphotypes show more complex patterns withenvironmental parameters, both in their abundance andaverage intra-morphotype size-variations (Renaud et al.,2002). Fine, qualitative morphological characters, like theshape of the suture lines and the central opening, were
proposed by Kleijne (1993) to discriminate between morphotypes. These characters are not normally targeted bymorphometric work. The most recent work, with data
emerging from life-cycle studies (Geisen et al., 2002) andmolecular biology (Saez et al., in press), conclusively
demonstrates the species character of Calcidiscus morphotypes and the taxonomy has been changed accordingly.
In the following pilot study, the objective was to test
the palaeoceanographical application of morphologicalvariability in C. leptoporus, by selecting three sites fromthe Canary Basin for a Holocene-LGM comparison.
Today, seasonal coastal upwelling offshore Morocco
results in an E-W fertility-gradient north of the CanaryIslands, including productive, upwelling-influenced surface-waters nearshore and oligotrophic surface-waters of
the subtropical NE Atlantic gyre further offshore. Annual
mean sea-surface temperatures (MSST) range from 17˚C
to 23˚C. During the LGM, atmospheric circulation wasenhanced over NW Africa (e.g. Sarnthein et al., 1981;
Hooghiemstra et al., 1987), which led to more intense
coastal upwelling in the studied area (see also Henderiks
et al., 2002 and references therein). Sea-surface temperatures were 4˚C to 6˚C lower than today (CLIMAP, 1981;
Henderiks & Bollmann, in review).

2. Material and methods
Four sites were selected from the Canary Basin for our
Holocene-LGM comparison (Figure 1a). Their locations
are given in Table 1, as well as all additional sediment
samples, representative of the Holocene and LGM time
periods, which were included in this pilot study. Gravity
cores and corresponding multi-cores from the Canary
Basin were taken during two CANIGO cruises with R/V
Meteor in 1996 and 1998 (M38/1 and M42/4; Wefer et al.,1997, 1999). Time control is based on oxygen isotope
stratigraphy and radiocarbon dating (Moreno et al., 2001
- GeoB 5559; Freudenthal et al., 2002 - GeoB 4216;
Henderiks et al., 2002 - GeoB 4241, 4242). Coccolithassemblages and their accumulation rates in the same
cores are described in Henderiks (2001). In the Canary
Basin, relative abundances of Coccolithus leptoporus are
between 3% and 6%, both during the Holocene and theLGM, and only minor glacial-interglacial variation inaccumulation rates was found for this species (Henderiks,
2001).

Figure 1: A) Detail of Canary Islands region, showing locations of gravity cores used and present day oceanographic and atmospheric circulation patterns. Seasonal coastal upwelling, driven by NE trade-winds during summer, occurs off Capes Ghir and Yubi. Dashed line depicts extent
of high pigment concentrations in surface-waters, most likely related to
upwelling, as observed by satellite (Davenport et al., 1999). Note darkgrey area outside today’s coastline, showing presumed exposed shelfarea, and glacial coastline, during glacial sea-level lows. B) Location of
additional sediment samples representing Holocene (open symbols) andLGM (filled symbols) time-slices, as well as the BATS Hydrostation-S
time-series and NABE-48 sediment trap deployments (stars) consideredin this study. For sample location details, see Tables 1a-1b

Coccolith size increase of Calcidiscus leptoporus

3

2.1 Sample preparation and morphometric measurements
Coccolith analyses of sediment samples were con(GeoB)(North)(West)
ducted with a Hitachi S2300 Scanning Electron
Microscope (SEM), at ETH-Z. A subsample of fineT88-9P
48˚23.2' 25˚05.6' 3193 13.78
0.537
fraction sediment (<38µm) was put in suspension
with denaturated alcohol and sprayed on a coverN3KF-21 42˚09.0' 12˚10.0' 4560 15.91
0.304
glass (after Bollmann et al., 1999). After drying, thecoverglass was mounted on an aluminium sampleGeoB 4216 30˚37.8' 12˚23.8' 2324 19.31
0.313
holder and sputtered with gold prior to SEM analyGeoB 4242 29˚40.5' 17˚53.3' 4286 20.78
0.214
sis.
GeoB 5559 31˚38.7' 13˚11.2' 3177 19.54
0.263
Morphometric measurements of Calcidiscus leptoporus coccoliths in these samples were carried out
V23-9823˚07.2' 19˚18.0' 3506 21.06
1.050
following Knappertsbusch et al. (1997), using themethod described by Bollmann (1997), with minor
Table 1a: Holocene surface sediment samples used in this study.
modifications. Slowscan SEM images were digitised
Modern annual MSSTs and chlorophyll concentrations given per locausing analySIS software (version 3.00), resulting intion from World Ocean Atlas (Levitus et al., 1998). Sample identifica768x576 pixel images. All specimens were analysed at ation includes ship, cruise and core number. T = R/V Tyro, APNAP-II(van Kreveld et al., 1996); N = NORESTLANTE III, Instituto
magnification of 8000x, which resulted in a pixel-size of
Hidrografico of Portugal; V = VEMA, Lamont-Doherty Geological
0.0241µm. Using a mouse-driven cursor, the diameter ofObservatory; GeoB = Meteor cores from the University of Bremen
every placolith wasmeasured, and the numCore
Lat.
L o n g . Water S a m p l e A g e
Reference
ber of radial elements
depth depth
counted, on digitised(GeoB)(North) (West)
(m)
(cm)
(kyr)
(Age Model)
SEM images of at least
30 specimens.
GeoB 4242 29˚40.5' 17˚53.3' 4286
93
20.2 Henderiks et al. (2002)
Planktonsamples
GeoB 4241 29˚10.0' 15˚27.1' 3609
4318.7 Henderiks et al. (2002)(collected on 47µm
GeoB 5559 31˚38.7' 13˚11.2' 3177
48
19-21 Moreno et al. (2001)
Millipore filters with
GeoB 4216 30˚37.8' 12˚23.8' 2324
78
17.9 Freudenthal et al. (2002)
0.45mm pore-size) were
GeoB 1048 20˚54.8' 19˚43.2' 3635
78
17.8 Henderiks & Bollmann (subm.)
analysedusingaPhillips XL30SIS SEM,
Table 1b: Selected gravity cores used for the analysis of C. leptoporus
at ETH-Z. Full details of the plankton sampling methodmorphology during the LGM
are given in Haidar et al. (2000). Images of C. leptoporus
Additional Holocene sediment samples (see Figure coccospheres, and any additional loose coccoliths, were1b), taken to the north of the main area of investigation, recorded digitally at a magnification of 3000x or 6000x
were kindly supplied by the Instituto Hidrografico of (see Renaud & Klaas, 2001 for details).
Core

Lat.

Long.

Water MSST C h l o r o depth
phyll
(m)
(˚C)
(µmole/l)

Portugal (N3KF21) and the Vrije Universiteit, Amsterdam(T88-9P; see van Kreveld et al., 1996). Relative abundances of C. leptoporus in these samples are highest, with
17% and 12%, respectively (Henderiks, 2001). To thesouth, two sites offshore Cape Blanc, within today’s centre of perennial coastal upwelling off NW Africa, wereanalysed for the Holocene (V23-98; Bollmann, 1997) andLGM (GeoB 1048) time-slices.
We compare the glacial-interglacial variability in coccolith morphology to modern seasonal changes observedin plankton samples from the Bermuda time-series(BATS) Hydrostation-S (Renaud & Klaas, 2001).
Samples used are representative for summer (17th July,
1991) and winter (29th January, 1992), both taken fromabout 25m depth (Haidar & Thierstein, 2001). In addition,
two samples from the NABE-48 sediment trap were
included, representing the (1) post-bloom summer (25thJuly, 1989) and (2) spring bloom (26th March, 1990) seasons (data from Renaud et al., 2002; Figure 1b).

3. Results
3.1 Morphology in Holocene assemblages
The frequency distribution of diameter and number of elements of all Calcidiscus leptoporus coccoliths in
Holocene sediments is bimodal (Figure 2). The frequency
of coccoliths with a diameter of between 6 and 7µm, andwith 20 to 22 radial elements, is the highest (Figures 2a,c). Morphometric data of individual samples are given in
Appendix A (Holocene), in which the bimodal distribution with an inflexion point at around 8µm, as observedby Knappertsbusch et al. (1997), is clearly expressed.
Sample means are given in Table 2. The smallest sizes
and numbers of elements were encountered in sample
T88-9P (mean diameter (D) = 6.24µm; mean number of
elements (E) = 19.6), which underlies surface-waters withmodern MSSTs below 14˚C. Samples taken in the vicinity of coastal upwelling regions off Cape Ghir (Morocco:
GeoB 5559 and 4216) and Cape Blanc (Mauritania: V2398) display similar, small mean-sizes (of about 7.3µm)

3.3 Seasonal morphological variability
The seasonal variability in morphology of living
Calcidiscus leptoporus at the Bermuda time-series station(BATS) is described in detail by Renaud & Klaas (2001).
Two main periods could be recognised: 1) from January to
April, a mixture of both ‘intermediate’ (5-8µm) and‘large’ (≥8µm) morphotypes were present throughout thephotic zone, down to 200m; and 2) from May and thereafter, the ‘large’ morphotypes disappear, but the ‘intermediate’ ones are present mostly in the upper 25m (Renaud

N=
Aver. Size
STDEV
stdev mean (95%)
Variance
Aver. Elements
STDEV
stdev mean (95%)
Variance
Time-slice

Oceanic

3.2 Morphology during the LGM
Scatter plots of morphometric data of all LGM samples
can be found in Appendix B (LGM). The frequency distributions of Calcidiscus leptoporus diameter and numberof elements measured in LGM samples are also bimodal(Figure 3), but show a distinct shift towards increased frequencies of larger coccoliths compared to the Holocene(Figure 2). This is also expressed in the sample means(Table 2, Figure 4a), which are larger during the LGM.
The largest glacial-interglacial size-difference occurred at
Sites GeoB 5559 and 4216, with mean-size increases during the LGM of 1.58µm and 0.92µm, respectively.
A significant increase in size of the largest specimens
within a sample is clear when the 75 percentile is considered, the measured size-value separating the largest 25%of the C. leptoporus coccolith assemblage from the smaller 75% (Figure 4b). An increase in size is also found in thesmallest 25% of coccoliths, although less pronounced (25percentile: Figure 4c).

NE Atlantic

Figure 2: Distribution of diameter and number of elements of all C. leptoporus coccoliths measured in the Holocene samples. A) Histogram ofcoccolith diameter (µm). B) Number of radial elements vs. coccolith
diameter. C) Histogram of number of radial elements. Note bimodal distribution of the histograms. Top right: SEM image of a single C. leptoporus coccolith illustrating morphometric measurements of diameter(D) and number of elements (E); this specimen contains 25 elements

Canary Basin

Nearshore

Cape Blanc

and mean numbers of elements (22-23).

Table 2: Morphometric measurements of C. leptoporus: sample means of size and number of radial elements. Grey columns denote samples corresponding to the
LGM time-slice

Henderiks & Renaud

GeoB
GeoB
GeoB
GeoB
GeoB
N3KF21 T88-9P 4242_01 4242_93 4241_43 5559_03 5559_48 4216_02 4216_73 V23-98 1048_78
51
55
56
54
51
48
58
49
31
58
51
6.92
6.24
6.78
7.43
7.50
7.28
8.86
7.35
8.27
7.25
7.22
1.36
1.02
1.05
1.79
1.52
1.48
1.77
1.31
1.51
1.55
1.65
0.37
0.27
0.28
0.48
0.42
0.42
0.46
0.37
0.53
0.40
0.45
1.84
1.05
1.11
3.21
2.30
2.19
3.14
1.70
2.27
2.40
2.71
21.22 19.62
20.84
22.43
23.08
22.00
26.28
23.10
25.45
22.66
22.33
4.14
3.06
3.80
5.82
5.65
5.41
5.79
4.76
4.87
4.79
4.97
1.14
0.81
1.00
1.55
1.55
1.53
1.49
1.33
1.71
1.23
1.37
17.17
9.39
14.46
33.87
31.95
29.32
33.50
22.68
23.72
22.90
24.75
HOL
HOL
HOL
LGM
LGM
HOL
LGM
HOL
LGM
HOL
LGM

4

& Klaas, 2001). The mean size and number of elements of
two typical ‘summer’ and ‘winter’ samples are plotted on
Figure 4a, as well as the means for three separate years.
The annual and summer means all plot within the range of
Holocene samples from the NE Atlantic, whereas the winter mean shows a large deviation from the same. The latter plots within the range of observations in sediment
samples from the LGM (Figure 4a).
This seasonal deviation in size is even more strongly
expressed if the 75 percentile is compared (Figure 4b).
For the 25 percentile, a less pronounced deviation in size
is observed (Figure 4c), but here also the winter value is5

Coccolith size increase of Calcidiscus leptoporus

Count

A

N=245

20

C. leptoporus coccolith assemblage from the larger 75% (25 percentile).
10

B

28

9
(r=0.72)

8
7
6
5
4

26

(r=0.70)

24
22
20
18
16

0

10

30

A
Mean # Elements

30(A), for the measured size-value separating the largest 25% of the C. leptoporus coccolith assemblage from the smaller 75% (75 percentile). C)
As (A), for the measured size-value separating the smallest 25% of the

Mean Diameter (µm)

larger than the one in summer. A comparable pattern was
found in sediment trap NABE-48, between the spring
bloom and summer seasons (Figure 4).
Figure 5 shows the relationship between mean coccolith size and number of elements with sea-surface temperature (SST) for Holocene sediment samples from thisstudy, and sediment trap (Renaud et al., 2002) and plankton assemblages from the Atlantic (Knappertsbusch et al.,
1997; Renaud & Klaas, 2001).

10

20

30

0

SST (oC)

0+ Plankton (Atlantic)

40

B

C

10

20

30

SST (oC)
NABE-48 (spring bloom)

BATS (winter)

NABE-48 (summer)

BATS (summer)

Holocene# Elements

35
Figure 5: Relationship between SST and A) mean coccolith diameter,
and B) mean number of radial elements for all Holocene sediment, seasonal sediment trap (NABE-48) and plankton (BATS) samples, as wellas additional plankton samples from the Atlantic (data from
Knappertsbusch et al., 1997; see legend). Although a positive correlation
exists between the Holocene mean morphological features and temperature (solid lines), the opposite appears for the seasonal samples (dashedlines)

30
25
20
15
10
0

5

10

15

0

20

Diameter (µm)

40

Count

Figure 3: Distribution of diameter and number of elements of all C. leptoporus coccoliths in samples corresponding to the LGM. A) Histogramof coccolith diameter (µm). B) Number of radial elements vs. coccolith
diameter. C) Histogram of number of radial elements. Note bimodal distribution of both histograms, and significant increase in larger coccoliths
compared to Holocene (Figure 2)

Mean # Elements

30

A

28

+ Annual mean BATS
BATS (winter)

26

BATS (summer)

24

+
++

22

NABE-48 (spring bloom)
NABE-48 (summer)

20

Holocene

18

LGM

16
5

6

7

8

9

10

Mean Diameter (µm)
34

C

28

30

# Elements# Elements

30

B

32

28
26
24
22

26
24
22
20
18

(75 Percentile)

20
6

7

8

9

10

Diameter (µm)

11(25 Percentile)

16
5

6

7

8

9

10

Diameter (µm)

Figure 4: A) Mean number of elements vs. mean diameter of all samples
considered in this study, including plankton (BATS), sediment trap
(NABE-48), Holocene and LGM sediment samples (see legend). B) As

4. Discussion
Knappertsbusch et al. (1997) found that the relative frequency of larger coccoliths (≥8µm) within Holocene surface sediments increased in tropical samples. Averagecoccolith diameter showed a distinct step towards larger
size at about 24˚C, resulting in an overall positive correlation between mean size and annual MSST (r = +0.530;
Knappertsbusch et al., 1997, tab.7). Mean coccolith size
also appears to increase with increasing MSST, within thetemperature range we studied in the NE Atlantic (14˚21˚C; Figure 5).
If these observations from Holocene sediments were
to be used to predict morphological characteristics ofCalcidiscus leptoporus coccoliths during the LGM in the
Canary Basin, when surface-waters were up to 6∞C colder in the investigated area (CLIMAP, 1981; Henderiks &Bollmann, in review), a decrease in the contribution oflarge coccoliths would be expected. Consequently, also adecrease in the mean size would be predicted. However,
the opposite was found in this pilot study. Mean coccolithsize, as well as the size of the largest specimens within
LGM samples, was significantly larger than within their
Holocene counterparts, especially in Cores GeoB 4216
and 5559. Figure 6 illustrates the reversed relationshipbetween MSST and mean coccolith size, with estimatedMSSTs for the LGM in each sample based on theGephyrocapsa palaeotemperature proxy (Henderiks &Bollmann, in review).
The main question is, therefore, to assess whether theobserved glacial-interglacial variability in coccolith size
could be explained by environmental processes, or6Henderiks & Renaud

whether they occurred due to other processes, such as sediment reworking and/or coccolithophore evolution.
Reworking of coccoliths from the Pliocene/Early
Pleistocene may have induced larger coccoliths of thespecies Calcidiscus macintyrei (Bukry & Bramlette,1969) Loeblich & Tappan 1978, with a last occurrence at
1.54Ma (see Hine & Weaver, 1998 for overview). In general, coccoliths of this species are larger (>10µm) thanthose of C. leptoporus (Knappertsbusch et al., 1997).
However, no specimens of Discoaster spp. were found in
the same samples and, therefore, extensive sediment
reworking from the Early Pleistocene can be excluded.
In this pilot study, and in the following discussion, thefocus lies on the first objective, ecological response, bycomparing data from the plankton and sediment traps
with our findings in the sediment.

Mean Diameter (µm)

10
9
8
7
6

(r=-0.89)

5

LGM

4
10

15

20
o

Est. SST ( C)
Figure 6: Mean diameter of C. leptoporus in samples corresponding to
the LGM in relation to the estimated SSTs for the same samples basedon Gephyrocapsa morphometry (Henderiks & Bollmann, in review).
Note, again, a reversed correlation (dashed line) in comparison to the
Holocene (Figure 5)

4.1 Seasonal variability in Calcidiscus
leptoporus morphology
Winter temperatures in the Sargasso Sea range between
19˚C and 21˚C, whereas temperatures reach 27˚C in summer. The annual range in SST in the Canary Islands region
today is 17-23˚C, i.e. within the winter range at BATS.
Therefore, we are not able to make absolute temperature
estimates based on the BATS-CANIGO comparison ofCalcidiscus leptoporus morphology (see Figure 5), especially not for the significantly colder LGM. The relationship of C. leptoporus morphology and SST remains
obscure, which is illustrated in Figure 7, where size distributions in the plankton, as well as our Holocene and LGM
sediment data, are plotted against temperature. However,
we can possibly deduce changes in seasonality of otherimportant oceanographic parameters, i.e. nutrients, fromthe pattern observed. That is, assess the amount of ‘winter-type’ versus ‘summer-type’ C. leptoporus being added

to the sediment assemblages.
The glacial-interglacial pattern in the Canary Islands
region is compared to the seasonal pattern at BATS in
Figure 8. The similarity of the size distribution between atypical winter plankton sample at BATS and the LGM
sediment samples suggests that a change in seasonality
between the LGM and Holocene in the Canary Islands
region may be responsible for the observed shift in themean size of C. leptoporus. The larger coccoliths occur
only in winter and are distributed within the entire photic
zone at BATS (Renaud & Klaas, 2001). The winter condition in the Sargasso Sea is characterised by convective
mixing, associated with storm-fronts moving from North
America (Michaels & Knap, 1996), and by highest nutrient concentrations in the surface-waters. Enhanced inputof larger ‘winter’ coccoliths during the LGM, when winter conditions similar to those off Bermuda prevailed in
our area of investigation, would lead to a mixture of C.
leptoporus in the sediments with larger means.
In the Canary Islands region, deep mixing of the surface-waters in winter leads to coccolithophore blooms ina similar way (e.g. Sprengel et al., 2000 and references
therein). Additional nutrient input occurs in summer during coastal upwelling events, especially nearshore.
Highest fluxes of C. leptoporus were recorded in
February and March in sediment traps north of the CanaryIslands, related to the winter phytoplankton blooms, after
breakdown of seasonal (summer) stratification within theupper photic zone (Sprengel et al., 2000, 2002). Largest
coccoliths of C. leptoporus (>10µm) were encountered in
the same sediment traps in February to April, although theaverage diameter showed no distinct seasonal variation(Baumann & Sprengel, 2000). Very recently, Renaud etal. (2002) reported on the seasonal variability of C. leptoporus morphotypes and their relationship with environmental parameters in two additional sediment traps fromthe NE Atlantic (NABE-48 and NABE-34). In the northernmost deployment, NABE-48, highest absolute abundances of the large morphotype were found in cool (12˚16˚C) water-temperatures, when high nitrate (i.e. nutrient)contents prevailed (Figures 7, 8). This supports our
hypothesis that a change in seasonality, and hencechanged input of C. leptoporus coccoliths to the sediments, could explain the observed glacial-interglacial
variability in morphology. Using an empirical calibrationof C. leptoporus morphology in Holocene sediments withMSST alone proved to be inadequate, since reversed
trends were found not only in seasonal plankton and sediment trap studies (Figure 5), but also in this LGM timeslice study (Figure 6).
The average size of C. leptoporus assemblages
depends on the success of the individual morphotypes.
Depending on what part of the temperature gradient is
considered, a different mixture of successful morphotypes
is found. For instance, the stepwise increase to large C.
leptoporus in tropical samples (above 24˚C:
Knappertsbusch et al., 1997) may be a reflection of

7

Coccolith size increase of Calcidiscus leptoporus

A. Plankton

B. Sediments: Holocene

C. Sediments: LGM

NE Atlantic

CANIGO

Diameter (µm)

1515CANIGO - Cape Blanc

Cape Blanc

1010> 8 µm

5 < 5 µm

5

0
0

10

20

30

40

13

in situ Temperature (°C)

14

15

16

17

18

19

20

21

22 14

Modern Annual MSST (°C)

15

16

17

18

0

19

Estimated MSST (°C)

NABE-48 (Renaud et al., 2002)
BATS (Renaud & Klaas, 2001)
Atlantic (Knappertsbusch et al., 1997)

Figure 7: Histograms of C. leptoporus coccolith size vs. SST, comparing A) plankton data (against in situ SST) with B) Holocene sediment data(against modern annual MSST; Levitus et al., 1998) and C) sediment data from the LGM (plotted against estimated MSST; Henderiks & Bollmann,in review). Morphotype boundaries at <5µm and >8µm, as defined by Knappertsbusch et al. (1997), are indicated in graphs. Note increased amountsof large coccoliths during LGM

15

Seasonality

Climatic Variability

Diameter (µm)

10

5

0

Plankton

Sediment Traps

BATS

NABE-48

BATS (summer)
BATS (winter)

Sediments
GeoB4242

NABE-48 (summer)
NABE-48 (spring bloom)

GeoB5559

GeoB4216CANIGO (Holocene)
CANIGO (LGM)

Figure 8: Summary of main variability in morphology discussed in this study. Histograms of C. leptoporus coccolith size comparing the seasonalvariability (summer vs. winter/spring bloom) at BATS and NABE-48, and climatic variability (interglacial vs. glacial) in the Canary Basin at threelocations (GeoB 4242, 5559 and 4216). Note that the LGM sediment samples and winter/spring bloom samples display highly similar size-distributions

8

Henderiks & Renaud

decreasing success of the intermediate morphotype alone,rather than increased production of the larger morphotype. Below this threshold of 24˚C, both the intermediateand large morphotypes have a potential to dominate, andthe average size of the assemblage will depend on the relative success of both. In the NE Atlantic, this relative success appears to depend on the seasonal variations in nutrients, with significant increases of the large morphotype
during bloom conditions.

type coccoliths than during the Holocene. In contrast, offshore Cape Blanc, no significant variability in coccolith
size was observed between the Holocene and LGM samples (Figure 7, Table 2), supporting previous observationsof lowered glacial productivity in this area. In addition,
the glacial drop in temperature of maximal 4˚C (to about
18˚C: Henderiks & Bollmann, in review) in this area is
not reflected in a change in morphology of C. leptoporus
coccoliths.

4.2 Calcidiscus leptoporus morphology inthe context of LGM palaeoceanography
The reconstruction of glacial-interglacial variability ofcoastal upwelling, and related changes in palaeoproductivity off NW Africa, is currently being reassessed.
Various studies in this region have shown enhanced intensity of the trade-winds during the LGM (Sarnthein et al.,
1981; Hooghiemstra et al., 1987), resulting in higher
coastal upwelling and productivity than during the
Holocene (e.g. Sarnthein et al., 1982, 1988; Abrantes,
2000; Sicre et al., 2000; Freudenthal et al., 2002;
Henderiks et al., 2002). However, high glacial productivity appears geographically limited to the northernmost latitudes of the NW African upwelling system (north of
25∞N). Evidence for lowered glacial productivity was
found off Cape Blanc, in today’s centre of the perennial
upwelling system (Bertrand et al., 1996; Martinez et al.,
1999; Ternois et al., 2000; Zhao et al., 2000). Reportedly,
productivity records are highly influenced by local
oceanographic processes, and could be controlled byadvection from the shelf and/or offshore shifts of the
upwelling cells related to sea-level changes (Bertrand etal., 1996; Zhao et al., 2000). A glacial sea-level drop of
about 120m must have had major implications for theprocess of coastal upwelling. The cross-shelf morphologyof the NW African margin during the LGM would imply
an upwelling system more confined to the shelf edge (e.g.
Fütterer, 1983; See Figure 1a, in which the grey area represents exposed shelf area during the LGM).
In the Canary Basin, the greatest glacial-interglacialdifference in mean coccolith size, of 1.58µm, was foundat Site GeoB 5559, and to a lesser extent (0.92µm) at Site
GeoB 4216 (Table 2). Today, these sites are in the vicinity of areas with seasonally-increased pigment concentrations that are presumably related to the coastal upwelling
process (e.g. Davenport et al., 1999). Freudenthal et al.
(2002) gave evidence for increased activity of these filaments during glacial times, influencing the surface-waters
and export production to Site GeoB 4216 more directly.
Site GeoB 4242 is well outside the influence of coastal
upwelling, in the outer oceanic domain, and showed theleast glacial-interglacial variability in Coccolithus leptoporus morphology (0.65µm).
Considering all available data on C. leptoporus morphology, we therefore propose that an increase of nutrient
input during enhanced glacial coastal upwelling off
Morocco led to the production of more ‘winter/bloom’-

5. Conclusions
A plausible explanation for the overall size increase of
Calcidiscus leptoporus coccoliths in the Canary Islands
region during the LGM could be a change in coccolithophore productivity, which promoted the production oflarger ‘winter/bloom’-type C. leptoporus. The winter conditions found off Bermuda in the Sargasso Sea today
agree well with the proposed environmental conditions
during the LGM in the Canary Islands region.
Atmospherically-driven mixing of the surface-waters
makes nutrients available in the surface-waters of theSargasso Sea during the winter, which is the period inwhich the larger coccoliths were observed.
In the Canary Islands region, deep mixing of the surface-waters in winter leads to coccolithophore blooms ina similar way and, during these times, highest fluxes of C.
leptoporus, as well as largest coccoliths, were found in
sediment traps (Sprengel et al., 2000; Baumann &Sprengel, 2000). Additional nutrient input occurs in summer during coastal upwelling events, especiallynearshore.
Enhanced coastal upwelling off Morocco during theLGM, due to the intensification of the trade-winds, led toeven higher input of nutrients to the photic zone andwould have lowered the seasonal variability in environmental parameters that determine the morphological characteristics of C. leptoporus coccoliths. Nevertheless, additional morphometric research on plankton samples fromthe Canary Islands region is necessary to further constrain
present day seasonal variability of C. leptoporus size in
the Azores and Canary currents.
Acknowledgements
H.R. Thierstein and K. von Salis are thanked for their supportand useful comments on this pilot study. This is a contribution to
the EC-MAST program CANIGO (Subproject 3, ‘Particle Flux
and Oceanography in the Eastern Boundary Current system’),EC Contract No. MAS-CT96-0060. JH was funded by the Swiss
Federal Office for Education (BBW No. 95.0355). SR was funded through the EC-TMR project CODENET - Coccolithophorid
Evolutionary Biodiversity and Ecology Network (FRMX-ET970113).

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11

BATS
(summer)

NABE-48(summer)

20

30
25
20

15

10

10

10

15

0

10

15

30
25
20

10
0

5

10

15

0

Diameter (µm)
15

10

10

10

10

5
0
40

0
40
GeoB 5559(Holocene)

25
20
15

30
25
20
15

10
5

10

Diameter (µm)

15GeoB 4216(Holocene)

30
25
20

5

10

Diameter (µm)

15

V23-98(Holocene)

30
25
20
15

10
0

15

5

35

15

10
0

10

0
40

35

# Elements# Elements

35

30

5

# Elements

GeoB 4242(Holocene)

35

Count

15

Count

15

0
40

5

Diameter (µm)

15

5

N3KF21(Holocene)

15

Diameter (µm)
Count

Count

Diameter (µm)

5

5

35

20

15
5

T88-9P(Holocene)

25

10

10

0
40

30

15
0

# Elements

535# Elements# Elements

25

10

0
40

35

30

Count

5
0
40

35

# Elements

1015# Elements

10
0
40

15

Count

15

40
30
20

Count

Count

Coccolith size increase of Calcidiscus leptoporus

10
0

5

10

Diameter (µm)

15

0

5

10

15

Diameter (µm)

Appendix A: Distribution of coccolith diameter and number of elements of all C. leptoporus in Holocene sediment samples, as described in thisstudy. For comparison, the seasonal summer samples from BATS and NABE-48 are included (Renaud & Klaas, 2001; Renaud et al., 2002)

Henderiks & Renaud

15

15
10

10

5
0
40

5
0
40

BATS
(winter)

25
20

25
20
15

10

10
15

Diameter (µm)

10

15

0
10

5
0
40

GeoB 4242
(LGM)

25
20
15

30
25
20
15

10
10

Diameter (µm)

15

5

10

Diameter (µm)

155GeoB 1048
(LGM)

35

30
25
20

30
25
20
15

10
0

15

0
40
GeoB 4216
(LGM)

15

10
5

5

35

# Elements# Elements

30

10

10

0
40
GeoB 5559
(LGM)

35

5

Diameter (µm)
Count

Count

Count

5
0
40

# Elements

5

10

0

20

Diameter (µm)

10

35

25

10
0

Count

10

30

15

# Elements

5

GeoB 4241
(LGM)

35

30

15
0

NABE-48(spring bloom)# Elements

30

5
0
40

35

# Elements

35# Elements

10

Count

20

Count

Count

12

10
0

5

10

Diameter (µm)

15

0

5

10

15

Diameter (µm)

Appendix B: Distribution of coccolith diameter and number of elements of all C. leptoporus in sediment samples corresponding to the LGM, as
described in this study. For comparison, the seasonal winter sample from BATS and spring-bloom sample at NABE-48 are included (Renaud &Klaas, 2001; Renaud et al., 2002)