Holocene lake-level changes in N- and S-Germany A. Kleinmann

Holocene lake-level changes in N- and S-Germany

A. Kleinmann ¹ , J. Merkt ² , H. Müller ² & H. Küster ¹

1

Institute of Geobotany, University Hannover

2

Geological Survey of Lower Saxony, Hannover

Berlin

Hämelsee

Hannover

Degersee

Lake-level fluctuations in Hämelsee SW-NE core transect

9

II I V

I Vc b a VI

a b c II

IVc b a V

14 10

c

8 15

?

7/2 7/1

I V

a b c V

16

a b

008 007

12 13 11

14 15 16 10 9 8 7 6 5 4 3 2 1

17 18

20 19

21

F IX

F Vb F VIII

F VII F VI F Vc F Va F IVc F IVb+a F III F II F I F X

[m]

lake level

lake level

low high ^II

III 11560 IVab IVc 11160

10660 Va

10155 9827 Vb VI

9220 Vc

12700 7970 VII

5660 VIII

FIRBAS zone cal years BP

0 20 40 60 80 100 120 % 80 %

0 10 20 30 40 50 60 70

Daphnidae

0 3 6 9 %

Fe/Mn

0 20 40 60 80 100 120 140 160 180 50 %

Fe

O

-17 -16

0 10 20 30 40 -19

-18 -15 -14

Bosmina long.

-18 -17 -16 -15 -14

% 100 200 300 400 500

Cyanophyceae Staurastrum

0 200 400 600 8000 200 400 600

Ba/TiO

Sr/TiO

X W V

2

9 F X

Roman Bronze

F VIII F VII F VI F V FIV FIII/II/I

[m]

lake level

U

E-transect

The sedimentation line is today 2 m below the lake level. During the Preboreal it was 9 m below modern lake level.

... in Degersee

Lake level oscillations in the Hämelsee and Degersee are shown by hiatuses, sand layers, by changes of microflora & -fauna, isotopes and by geochemical evidence (redox, evaporation elements). The oscil- lations are climatically induced as the lakes are fed only by groundwater and precipitation. During the

upper Preboreal (IVc) the lake levels were temporarily lowered by 5-7 m. The level of Hämelsee was also lower than at present in the upper Boreal (Vc), Atlantikum, Subboreal, Older Subatlantikum.

Hämelsee: Lake-level fluctuations during the Preboreal - detail of above diagram

250 %

Fe/Mn

0 30 60 90

-18.8 -18.7 -18.6 -18.5 -18.4 -18.3 -18.2 -18.1

%

Ba/TiO

0 900 0 2 4 6 8 10

Daphnidae

0 50 100 150 200

Cyanophyceae

10 20 30 40 50 60 %

Staurastrum

0

Bosmina l.

20 40 60 80 % 0

11160 cal BP 10800 cal BP

poorly developed varves

sediment reacts in 2 major steps: 18.63 and 18.58 m

= ~160 yrs later.

with about 20 massive, ochre coloured sideritic layers intercalated. They were precipitated during summer.

~160

re-establishment of fully developed varves, anoxic conditions

well developed varves perfect sideritic varves

-9-8-7-6-5-4-3-2-1-0 1

-18.8 -18.7 -18.6 -18.5 -18.4 -18.3 -18.2 -18.1

d

O

d

C

-10 -7 -4 -1

[m]

profundal section [m]

This study was supported by the Deutsche Forschungsgemeinschaft within the SPP " Change of the Geo- and Biosphere during the last 15000 years" (Me 1371/1-3, Ku 599/12-4). We thank B. Mayer, Calgary, who is responsible for the stable isotope analyses.

Hämelsee