Invigoration of Southern Ocean surface circulation during Late Eocene cooling

Invigoration of Southern Ocean surface circulation during Late Eocene cooling

Sander Houben ^1,2 , Peter Bijl ¹ , Appy Sluijs ¹ , Stefan Schouten ³ , Henk Brinkhuis ³

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

3 4 5 6 7 8 9 10 11 12 13 14 16 15

17 18 20 Core

Depth (mbsf)

Nannofossil diatomaceous ooze with glauconite horizons

Nannofossil-diatomaceous ooze

Diatomaceous

ooze with sands, higher glauconite content

DSDP Site 511

(Falkland Plateau, South Atlantic)

545 550 555 560 565 570 575 580 585 590 595 600 605 610 615 620 625 630

Depth (mbsf)

VIID VIIC VIIB

2a Unit Age

61 60 59 58 57 56 55 54 53

Organic-rich sandy mudstone Glauconitic sandy-silty mudstone Grey clayey mudstone

Rounded dropstones

ODP Site 696

(Northwestern Weddell Sea)

80 100 120 140 160 180 200 220 240 260 280 300 320 340 360 380 400

IVB IVA III IIC IIB IIA

Siliclastic clayey siltstone Glauconitic calcareous clay

Siliclastic silty claystone Glauconite-rich sandstone Siliceous chalk with

Depth (mbsf)

ODP Site 1128 (Great Australian Bight)

Core Unit Age Unit Age

Brown’s Creek Clay Notostrea Gs.Turritella clayBanded Bryozoal MarlsTurritella clay

Browns Creek (Victoria, Australia)

Sandstone with carbonaceous beds Ferruginous sandstone

Fining upward organic-rich silty claystone with Turritella shells

Glauconite-rich sandstone with abundant Notostrea shells Carbonaceous grey clay

Subunit IIIA:

Organic-rich claystones Transitional interval IIIA:

up-section increase in glauconite Unit II: Glauconite-rich clay- and siltstone

Transitional chalk:

up-section increase of CaCO₃ Unit IC: Carbonate ooze

ODP Site 1172 (East Tasman Plateau)

Alterbidinium distinctum Schematophora speciosa

Reticulofenestra oamaruensis (NF) Deflandrea sp.A

Deflandrea sp. A

LCO Enneadocysta diktyostila

Schematophora speciosa Stoveracysta ornata Malvinia escutiana

Phthanoperidinium amoenum

LAO Phthanoperidinium sp. A

ĺ

Stoveracysta kakanuiensis Stoveracysta kakanuiensisMalvinia escutiana

Alterbidinium distinctum

Abundant Phthanoperidinium sp. A

ĺ

Enneadocysta pectiniformis Hystrichosphaeridium tubiferum Hystrichokolpoma truncatum Schematophora obscura Rhombodinium draco

Barren

Reticulatosphaera actinocoronata Stoveracysta kakanuiensis Dinocyst sp. 1

Dinocyst sp. 2 Oligokolpoma galeottii Operculodinium tiara

Aireiana verrucosa Dinocyst sp. 2

Corrudinium regulare

Schematophora speciosa Hemiplaciphora semilunifera

ĺ

Schematophora speciosa Operculodinium tiara

Reticulatosphaera actinocoronata Stoveracysta ornata

Stoveracysta kakanuiensis Dinocyst sp. 1

Aireiana verrucosa

Onset of ‘greensand deposition’

Correlative level of the Oi-1 shift

Acaranina collactea (PF) Pseudohastigerina micra (PF)

Stoveracysta ornata

FAO Phthanoperidinium sp. A Rhizosolenia oligocaenica (D)

Istmolithus recurvus (NF)

early Oligocenelate Eocene Istmolithus recurvus (NF)

early Oligocenelate Eocene middle Eocenelate Eoc.early Oligocene late Eoceneearly Olig.

Unconformity

Height (m)

Johanna River Sand

ĺ

0 10

5 15 20 25 30 35

ĺ

Achomosphaera alcicornu

ĺ

355

360

365

370

Depth (mbsf)

IIIA II IC

C17nC16n.2nC16n.1nC13rC11n

Unit Age

Deflandrea sp. A, Stoveracysta ornata Oligokolpoma galleottii

Schematophora speciosa

Alterbidinium distinctum Deflandrea sp. A

Stoveracysta ornata

Stoveracysta kakanuiensis

Aireiana verrucosa Schematophora speciosa

ĺ

Barren

Chron

late Eoceneearly Oligocene Barren

Achomosphaera alcicornu

ĺ

Unit Age

First/Lowermost Occurrence Last/Uppermost Occurrence Reticulatosphaera actinocoronata

Ma (Sub)Epoch

30.5 31 31.5 32 32.5 33 33.5 34 34.5 35 35.5 36 36.5 37 37.5 38 38.5 39 39.5

Late EoceneEarly OligoceneMiddle Eocene (Sub)Chron C13n

C15n

C16n.1n C16n.2n

C17n.1n

C17n.2n C17n.3n

C18n.1n C18n.2n C12n

C12r

C13r

C15r C16n.1r

C16r

C17r

40

Abstract

353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372

20 21 22 23 24

0.0 0.2 0.4 0.6 0.8 1.0

0 20 40 60 80 100

ODP Hole 1172D

IIIA II IC

C17nC16n.2nC16n.1nC11n.2nC11n.1nC13nC15n

ĺ ĺ

Sea Surface Temperature (°C)

BIT-Index

% High latitude dinocysts (trans-Antarctic and bioplar taxa)

0 20 40 60 80 100

% Brigantedinium spp.

Depth (mbsf)

Litho-Unit Mag-Strat

Oi-1

10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190

3 4 5 6 7 8 9 10 11 12 13 14 16 15

17 18 20 Core

Depth (mbsf)

2a

Litho-Unit

0.0 1.0 2.0

5 10 15 20 25

DSDP Site 511

0 20 40 60

% Brigantedinium spp.

Sea Surface Temperature (°C)

į¹⁸O_Subbotina (‰VPDB)

early Oligocenelate Eocene

Oi-1

LO S. speciosa

S. speciosa present FO S. speciosa

Barren of organics

36.5 36.3 35.7 35.6 35.4 34.8 33.7 29.9

Age (Ma)

30.2

35.4

35.5 34.5 33.7 32.5

Age (Ma)

LO S. speciosa

TEX₈₆^H

TEX₈₆^H U^k’₃₇

0 20 40 60 80 100

% perinioid + protoperidiacean dinocysts

511

696

Browns Creek 1128

1168 1172

511

1172

696

Browns Creek 1168 1128

511

1172 Browns Creek 1128

1168

1090

277

739

U1356 CRP-3

early late Eocene (36 Ma) latest Eocene (34 Ma) early Oligocene (32 Ma)

Cosmopolitan and high-latitude autotrophic dinocysts dominant High-latitude endemic dinocysts dominant

Abundant high-latitude dinocysts and protoperidiniacean dinocysts Protoperidiniacean dinocysts dominant

Diverse, autotrophic dinocyst assemblage

696 739

Tools

Stratigraphy and lithology

Absolute SST

Synthesis and conclusions

1 MPP, Utrecht University, Utrecht, the netherlands; 2 Geological Survey of the Netherlands, Utrecht, the Netherlands; 3 Royal NIOZ, and Utrecht University, Texel, the Netherlands

The Late Eocene (37-34 Ma), progressive cooling preconditioned Antarctica for glaciation. Questions remain about the exact oceanic reorganisations that occurred in the Southern Ocean, as a result of tectonic gateway opening, and the consequences for regional tem- perature. We have reviewed the available sediments covering the Late Eocene, which we could accurately correlate stratigraphically.

We reconstruct profound ocean current invigoration leading up to Antarctic glaciation, which had major consequences for regional dis- tribution of heat particularly in the southwest Pacific Sector.

We use dinoflagellate cysts preserved in a number of sedimentary archives in the Southern Ocean. Eocene dinocyst assemblages are dominated by an Antarctic endemic community in sediments under- lying Antarctic-derived surface currents (Bijl et al., 2011).

In 2 key sectors, the southwest Pacific (Site 1172) and sw Atlantic Ocean (Site 511), we pair our dinocyst analyses with organic geo- chemical biomarker analyses (TEX ₈₆ and U ^K ’ ₃₇ ) for quantitative sea surface paleotemperature reconstructions.

Using particularly dinoflagellate cysts, we could stratigraphically correlate coarse- grained green- sand deposits around the Antarctic Margin and on the South Australian Margin. This suggests throughout the Southern Ocean, surface currents invigorated, probably as a result of stronger at- mospheric circulation forced by progressive cool- ing, and possible some glaciations on Antarctica.

Not only the Antarctic Counter Current invigorated in this process, but also the Proto-Leeuwin Cur- rent, flowing south of Australia.

Site 1172 in the sw Pacific Ocean, shows the onset of throughflow of the proto-leeuwin current in the di- minishing abundance of endem- ic-antarctic dinocysts. The surface water warming as documented in TEX ₈₆ suggest that the incoming proto-leeuwin water was signifi- cantly warmer than the Antarc- tic-derived Tasman Current water.

SSTs at Site 511 in the sw Atlantic Ocean show a much more ‘classic’

cooling pattern across the Eo- cene-Oligocee boundary, suggest- ing no changes in Drake Passage

throughflow. The late Eocene Southern Ocean saw a series

of powerful positive climate feedbacks: gateway deepening, climatic cooling, atmospheric circu- lation, thermal isolation and biological productiv- ity.

These may have been a preconditioning factor in the nature and timing of ice-sheet expansion across the Oi-1, which is considered to be ulti- mately forced by decreasing atmospheric CO2 concentrations and orbital forcing of summer in- solation.

Intensification of the Antarctic Counter Current and its feedbacks may have contributed to set- ting the stage of minor scale, ephemeral Antarc- tic glaciations prior to the EOT.

1

2

3

Fig. 1. Lithologies and stratigraphic correlation of sedimentary records around Antarctica.

Fig. 2. biomarkers and dinocyst assemblages of 2 key sites: 1172 in the sw Pacific Ocean and Site 511 in the sw Atlantic Ocean.

Fig. 3. Synthesis of oceanographic changes in the Southern Ocean

across the Eocene-Oligocene boundary