Sapropels S1, S3, S4 and S5 in the Ionian Sea: a study based on dinoflagellate cysts
Michelle de Groot*[a], Karin Zwiep [a], Timme Donders [b],
Alessandra Negri [c], Caterina Morigi [d]; Joerg Keller [e], Francesca Sangiorgi [a]
Introduction
The Eastern Mediterranean late Neogene to Quaternary sedimentary record is characterized by the distinct quasi-periodical occurrence of organic carbon-rich layers, called sapropels (Fig. 1). Their deposition is related to significant chang- es in climate, in the pattern of water circulation and in the biogeochemical
cycles. In general, an increase in organic matter preservation at the seafloor due to hypoxia or anoxia and enhanced productivity in surface waters are indi- cated as two major contributing factors for sapropel formation. While the trig- gering mechanism for sapropel formation is still debated, it is clear that each sapropel has its own peculiar feature (review in 1).
Material & Methods
Samples are from core M25/4-12 collected in the Ionian Sea core (Fig. 1). Sam- ples across sapropel S1, S3, S4 and S5 were taken at 1 cm resolution and ana- lyzed for palynology (dinoflagellate cysts) and Total Organic Carbon (TOC)
weight percentage.
20 22 24 26 28 30 32 34 36 38
40
20 40 60 80 100
Total heterotrophic dinocysts Brigantedinium spp.
15 30
Selenopemphix nephroides
8
Polysphaeridium zoharyi
10 20
Spiniferites spp.
10 20
Bitectatodinium tepikiense
8
Operculodinium centrocarpum
10 20
Nematosphaeropsis labyrinthus
20 40 60 80
I mpagidinium spp.
I mpagidinium aculeatum
25000 50000
Total dinocysts/gr. sed.
Total heterotrophic/gr. sed.
Depth (cmbsf)
412 414 416 418 420 422 424 426 428 430 432
0 20 40 60 80
Total heterotrophic dinocysts Brigantedinium spp.
0 15 30
Pentapharsodinium dalei
0 1
P. zoharyi
0 20 40 60
Tuberculodinium vancampoae
0 2 4
Lingulodinium machearophorum
0 15 30
Spiniferites spp.
0 2
Spiniferites elongatus
0 2
B. tepikiense
0 5
O. centrocarpum
0 10 20
N. labyrinthus
0 20 40 60 80
I mpagidinium spp.
I . aculeatum
0 5
I . sphearicum
0 20 40 60 80
I . patulum/ paradoxum
0 25000 50000
Total dinocysts/ gr. sed.
Total heterotrophic/gr. sed.
Depth (cmbsf)
600 602 604 606 608 610 612 614 616 618 620 622 624 626 628 630 632 634 636 638 640
0 20 40 60 80
Total heterotrophic dinocysts Brigantedinium spp.
0 10 20
S. nephroides
0 5
P. zoharyi
0 4 8
T. vancampoae
0 4 8
L. machaerophorum
0 20 40 60 80
Spiniferites spp.
0 20
S. pachyderma
0 4
S. elongatus
0 15 30
B. tepikiense
0 10 20 30 40
O. centrocarpum
0 30 60
N. labyrinthus
0 5 10
Pyxidinopsis reticulata
0 50 100
I mpagidinum spp.
I . aculeatum
0 25000 50000
Total dinocysts/ gr. sed.
Total Heterotrophic/gr. sed.
Depth (cmbsf)
500 505 510 515 520 525 530 535 540 545 550
Depth (cmbsf)
0 30
Total heterotrophic dinocysts Brigantedinium spp
0 20
L. machaerophorum
0 20 40 60
Spiniferites spp.
0 10
S. elongatus
0 10
B. tepikiense
0 20
O. centrocarpum
0 20 40
N. labyrinthus
0 20 40 60 80
Impagidinium spp.
I. aculeatum
0 10
Impagidinium velorum
0 5000 10000 15000
Total dinocysts/gr. sed
Total heterotrophic/gr. sed
S1
S3
S4
S5
Fig 1. Location (A) and log (B) of the core M25/4-12 in the Ionian Sea at 2500 m water depth (2) . The age (kyrs BP) of the 10 most recent sapropels in shown in C(3)
Fig 2. Dinocyst assemblages in sapropels S1, S3, S4 and S5.
Sapropel layer Tephra layer Oxidized layer?
Utrecht University [a] Department of Earth Sciences, Utrecht University, The Netherlands; [b] Department of Physical Geography, Utrecht University, The Netherlands; [c] Department of Life and Environmental Sciences, Polytechnic University Marche, Italy;
[c] Department of Geology, University of Pisa, Italy; [d] Institut für Geo- und Umweltnaturwissenschaften, Freiburg University, Germany
The percentage of heterotrophic dinocysts, mainly Brigantedinium spp., in- creases in all sapropels, suggesting higher productivity and/or enhanced preservation during sapropel formation5.
Dinocyst concentration (dinocysts/gram sediment), another indicator for pri- mary productivity, increases in all sapropels.
S4 has the lowest dinocyst diversity, and lowest concentration of both total dinocysts and mainly heterotrophic dinocysts. Given the sediment accumula- tion rate, S4 seems to have the lowest productivity
Both sapropel S1 and S5 show highest percentages of cold-loving species (Bi- tectatodinium tepikiense and Spiniferites elongatus)6 mostly before sapropel deposition and during the their lower part
A thin layer with abundant B. tepikiense seems to indicate S5 interruption. In contrast, the upper part of S5 has abundant warm-loving species (Spin- iferites pachyderma).
Sapropel S3 and S5 contain Tuberculodinium vancampoae, which becomes very abundant in S3. T. vancampoae percentages of 10-30% are at present found in coastal bays of subtropical areas where winter temperature is ~17°C, summer temperature ~27°C and summer salinity lower than 35 psu6.
The lagoonal species Polysphaeridium zoharyi indicates warm conditions and high water stratification during the upper part of S5.
Duration (kyrs)4 Thickness (cm) SAR
(cm/kyr) TOC%
Sapropel S1 4.4 12.5 2.8 >1.4
Sapropel S3 4 10 2.5 >1.6
Sapropel S4 6.2 12.5 2.0 >1.5
Sapropel S5 7.4 24 3.2 >2
Table 1. Sapropel thinkness (cm), TOC (weight %) and sediment accumulation rate SAR (cm/kyr)
M.R.deGroot1@students.uu.nl
A. B.
C.
Take home message
• Sapropels S1, S3 and S5 all show high productivity, higher than in S4. Preservation seems to be very important during S1, but productivity remains high after sapropel termination
• Abundant Tuberculodinium vancampoae in S3 suggests warm year-round surface water temperatures and summer salinity lower than 35 psu.
• Dinocysts in S5 indicate relatively cold water conditions during the deposition of its lower part while warm stratified waters characterize the deposition of its upper part.
Results & Discussion
TOC percentage within all sapropels is always above 1.4%, indicating the expect- ed increase in organic carbon burial during sapropel deposition. S5 has the high- est TOC (Table 1).
References
1. Rohling et al. (2015) Earth-Science Reviews 143, 62-97 2. Negri et al. (1999) Marine Geology 157, 89-103 3. Emeis et al. (2003) Paleoceanography 18(1) 4. Grant et al. (2012) Nature, 491, 744-747
5. Versteegh & Zonneveld (2002) Geology 30(7), 615-618
6. Zonneveld et al. (2013) Review of Palaeobotany and Palynology 191, 1-198
