(Table 1, page 605) Chemistry of concretions from Grand Lake (GL) and Ship Harbour Lake (SH), Nova Scotia and Mosque Lake (ML), Ontario

Studies by optical microscopy, x-ray diffraction, and electron probe techniques of ferromanganese concretions from three Canadian lakes reveal chemical banding of amorphous hydrated iron and manganese oxides. The average ratio of iron to manganese in concretions from these lakes varies from 0.43 to 2.56. The concentrations of cobalt, nickel, copper, and lead are one to two orders of magnitude below those reported for oceanic ferromanganese concretions.

(Table I, page 1348) Composition of ferromanganese oxide concretions from lake Ontario (Extract)

A large deposit of ferromanganese oxide concretions has been found in the northern portion of Lake Ontario. The concretions occur mainly in the form of coatings on sand grains but manganese nodules are present at several localities. Mineralogically, the ferromanganese oxide phases are amorphous, and their Fe and Mn contents are similar to those in concretions from other environments. However, their Ni, Co, and Cu contents are significantly higher than those reported in previously described North American lacustrine ferromanganese concretions, and this may, in part, be a reflection of their probable low rates of accumulation.

(Table 1, page 204), Minor element concentrations in nodules of lake Ontario at Glenola, Bay of Quinte

Spark source mass spectroscopy was used to analyze 61 elements in ten ferromanganese nodules found near Glenora in the Bay of Quinte at the eastern end of Lake Ontario. Most minor elements, including As, Pb, and Hg, have concentrations between 1-100 µg/g. F, S, Co, Zn, and La have concentrations in 100 µg/g range. Ba and Sr are present at levels of 1% and 0.1% respectively. Compared to similar measurements on nodules found in the Great Lakes and in other parts of the globe, values reported here are generally lower. Compared to their marine equivalents, lake nodules appear to be inferior scavengers of minor elements. Examination of all available data corroborates the postulate that marine biological material is an important source of minor elements found in oceanic nodules.

(Table 3, page 309) Mercury content of concretions from Grand Lake (GL) and Ship Harbour Lake (SH), Nova Scotia and Mosque Lake (ML), Ontario

Ferromanganese concretions from Grand Lake and Ship Harbour Lake in Nova Scotia and Mosque Lake in Ontario are most common in water 0.5 to 2 m deep. X-ray diffraction studies show the ferromanganese portions of the concretions to he amorphous. Petrographic and electron probe studies of the ferromanganese material reveal chemical banding of iron and manganese. Bulk chemical analyses indicate that the Fe:Mn ratios of concretions from different sites within a single lake are similar, whereas concretions from different lakes have characteristic Fe:Mn ratios. Trace element concs are different in different lakes and are generally several orders of magnitude less than those of oceanic nodules.

Lake Son Kol geochemistry, µXRF, biogeochemistry and pollen record

In general, a moderate drying trend is observed in mid-latitude arid Central Asia since the Mid-Holocene, attributed to the progressively weakening influence of the mid-latitude Westerlies on regional climate. However, as the spatio-temporal pattern of this development and the underlying climatic mechanisms are yet not fully understood, new high-resolution paleoclimate records from this region are needed. Within this study, a sediment core from Lake Son Kol (Central Kyrgyzstan) was investigated using sedimentological, (bio)geochemical, isotopic, and palynological analyses, aiming at reconstructing regional climate development during the last 6000 years. Biogeochemical data, mainly reflecting summer moisture conditions, indicate predominantly wet conditions until 4950 cal. yr BP, succeeded by a pronounced dry interval between 4950 and 3900 cal. yr BP. In the following, a return to wet conditions and a subsequent moderate drying trend until present times are observed. This is consistent with other regional paleoclimate records and likely reflects the gradual Late Holocene diminishment of the amount of summer moisture provided by the mid-latitude Westerlies. However, climate impact of the Westerlies was apparently not only restricted to the summer season but also significant during winter as indicated by recurrent episodes of enhanced allochthonous input through snowmelt, occurring before 6000 cal. yr BP and at 5100-4350, 3450-2850, and 1900-1500 cal. yr BP. The distinct ~1500-year periodicity of these episodes of increased winter precipitation in Central Kyrgyzstan resembles similar cyclicities observed in paleoclimate records around the North Atlantic, likely indicating a hemispheric-scale climatic teleconnection and an impact of North Atlantic Oscillation (NAO) variability in Central Asia.

Geochemistry on sediments in Lake Biwa

Thirty sediment cores (30-40 cm in length), 47 Ekman dredge sediments, and Mn concretions were collected from Lake Biwa. The concentrations of 36 elements in the samples were determined by instrumental neutron activation, X-ray fluorescence, atomic absorption, and colorimetric analyses. The elements determined included Mn, P, As, Sb, Fe, Ni, Co, Zn, Cu, Pb, Hg, Cr, Ti, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Sc, Hf, La, Ce, Sm, Eu, Yb, Lu, U, Th, Au, Ta, Nd, Br and N. Based on statistical considerations and calculation of the concentration factors of the elements, the features of the elemental distribution in Lake Biwa sediment were determined. The main results are summarized as follows : (1) Concentrations of Mn and As were very high in the uppermost oxidized layer of the offshore sediment and Mn concretions. This resulted from the dissolution-deposition cycles of these elements within the sedimentary column and the bottom water. The fixation of As at the sediment surface is mainly attributed to the adsorption of arsenate onto Mn (II) -rich hydrous Mn (IV) oxide. (2) There were high concentrations of Zn, Cu, Pb and Hg in the recent sediments. Although the source of these elements is attributed to human activities, the individual distributions of Zn and Cu in the sediment may result from the deposition of metal-rich planktonic debris and subsequent degradation of the debris. (3) The orders of increasing concentrations of alkali metals and lanthanides in the sediment from the central region compared with the nearshore pediment were identical to the orders of increasing atomic numbers from Na to Cs and from La to Lu, respectively.

Dead Sea lake level for the last 260 ka

The rain regime of the Levant during the late Quaternary was controlled primarily by Mediterranean cyclonic systems associated with North Atlantic climate shifts. Lake levels in the Dead Sea basin have been robust recorders of the regional hydrology and generally indicate highstand (wet) conditions throughout glacial intervals and lowstands (dry) during interglacials. However, sporadic deposition of travertines and speleothems occurred in the Negev Desert and Arava Valley during past interglacials, suggesting intrusions of humidity from southern sources probably in association with enhanced activity of mid-latitude Red Sea synoptic troughs and/or low-latitude tropical plumes. The southerly incursions of wetness were superimposed on the long-term interglacial Levantine arid conditions, as reflected by the current prevailing hyperaridity, and could have had an important impact on human migra- tion through the Red Sea-Dead Sea corridor.