Cold Climatic Periods Research Articles

Stability of water masses‐impact on cod recruitment off West Greenland

ABSTRACTBased upon the hypothesis of Meyer (1968: Hansa, 16:2–4) that periods of low stability of the water column in autumn should parallel good cod year‐classes in the following year, the paper analyzes available time series of cod recruitment, subsurface oceanographic stability data and wind stress data off West Greenland. No significant correlations were found between stability, wind stress and recruitment when considering the entire. length of available time series. However, splitting the autumn‐based oceanographic data set into a pre‐ 1970s part (when warm climatic conditions and high recruitment prevailed), and a recent part (for the past 20 years of cooling climate) yields significant coherence of recruitment and environmental conditions for the cold climate period. For the warm climate period, only occasional consistency is shown. The possible influence of the Great Salinity Anomaly on recruitment of cod is discussed. It is suggested that during the past 20 years a new correlation mechanism, an advective coupling instead of low stability coupling, may explain the variability of recruitment.

Carbonate preservation history in the Peru Basin: Paleoceanographic implications

We studied preservation/dissolution cycles and paleoproductivity in eight sediment cores from the Peru Basin south of the highly productive surface waters of the eastern equatorial Pacific. Stratigraphy is based on stable oxygen isotopes and on combined magnetostratigraphy and biostratigraphy. Sediment cores which span the last 8 m.y., were retrieved during cruise 79 with RV SONNE close to the carbonate compensation depth (CCD). In general, sediments show Pacific‐type carbonate cycles. We interpret a pronounced carbonate peak between 6 and 7 Ma as the result of a western and northern extension of the highly productive Peru Current. Decreased carbonate contents from the late Miocene to the late Pliocene might be associated with a slow contraction of the latitudinal extent of the high‐productivity belt north of the study areas. During the Pliocene, carbonate variations showed 400 kyr cycles indicating the growth and decay of ice sheets, which should have been associated with pulsations of the Antarctic ice cap. An abrupt collapse of the carbonate system occurred at 2.4 Ma. Higher frequency variations of the carbonate record indicate the major increase of the northern hemisphere glaciation. During the Quaternary, carbonate fluxes are high during glacials and low during interglacials. Large amplitude variations with long broad minima and maxima, associated with small migrations of the lysocline and the CCD (< 200 m), are indicative of the preservation/dissolution history in the Peru Basin. During the early Pleistocene, climatic forcing by the 41 kyr obliquity cycle is not observed in the carbonate record. During the last 800 kyr, variability in the carbonate record was dominated by the 100 kyr eccentricity cycle. Fluxes of biogenic material (calcium carbonate, organic carbon, opal, and barium) were greatest during glacials, which imply higher productivity and export production of the Peru Current during cold climatic periods. Dissolution was greatest during interglacials as inferred from the relatively poor preservation of planktonic foraminifera and from the low accumulation rate of carbonate. After the Mid‐Brunhes Event (400 ka), we observe a plateaulike shift to enhanced dissolution and to intensified productivity.

Cyclical patterns in the Pleistocene human occupation of Southwest Tasmania

AbstractOne hundred Pleistocene radiocarbon determinations from southwest Tasmanian archaeological sites are used to construct a moving sum of determinations every 500 years within periods spanning 1000 years. The resulting plot shows a cyclical pattern with an increasing amplitude through time. The cyclical pattern can be correlated with climatic indicators from Pulbeena Swamp (northwest Tasmania) and allows us to suggest that the archaeological sites were subject to relatively low levels of occupation during periods of cold and dry climate.

Heinrich events in the North Atlantic: radiochemical evidence

Heinrich events are a series of apparently synchronous sediment horizons in the North Atlantic with unusually high ratios of lithic fragments to foraminifera in the coarse fraction. They occur more prominently during cold climatic periods and could have been produced either by dramatic decreases in surface water productivity, by brief increases in carbonate dissolution on the seafloor, or by rapid accumulation of ice-rafted debris. The excess 230Th activity profile in core CHN82 31 11PC(42°23′N, 31°48′W) provides evidence in support of the last of these explanations for the two most recent events (H1 and H2). Sediment flux reconstruction based on the constant 230Th flux model indicates that sediment rain rates increased from an average of ca 1.6 g cm −2 ka −1 to at least 19 g cm −2 ka −1 during Heinrich event H1 and 11 g cm −2 ka −1 during Heinrich event H2. These estimates are lower limits, as bioturbation likely smoothed the 230Th profile. Our data also suggest a maximum of 600 y for the duration of H1 and 800 y for H2. Two independent approaches provide similar estimates of sediment mass accumulation (g cm −2) at the site during the two events; ca 10 g cm −2 and ca 9 g cm −2 were deposited from the overlying water column during event H1 and H2. An additional ca 4 g cm −2 were brought to the site by sediment focusing during event H1. These methods provide a means of mapping and quantifying IRD mass accumulation over the North Atlantic for studying the processes that controlled the distribution of the Heinrich deposits.

The drift of the Fennoscandian and Ukrainian Shields during the Precambrian: a Palaeomagnetic analysis

A revised Precambrian (2.85−0.6 Ga) Apparent Polar Wander Path (APWP) for the Fennoscandian Shield, based on a new compilation and analysis of data, is presented. In fitting the APW path to successive Grand Mean Palaeomagnetic poles (GMPs), we applied the spherical spline technique originally developed by Jupp and Kent in 1987. The position and orientation of the Fennoscandian Shield during 2.85−0.6 Ga was determined from the GMPs. Major palaeoclimatological findings are used to constrain the palaeomagnetic interpretation of palaeolatitudes. The general drift of Fennoscandia, from relatively high latitudes in the late Archaean-Early Proterozoic to nearly equatorial latitudes in the Middle Proterozoic, correlates with palaeoclimatological indications that a period of cold climate was followed by one of warm climate during this time interval. From the continuous APWP the APW velocities and latitudinal drift velocities of the shield were calculated. An accumulated APW curve was also calculated. The palaeomagnetic data are irregularly distributed and some periods are rather poorly represented. This means that the calculated velocities can sometimes be artifacts of sampling. Late Archaean and Early Proterozoic (2.85−1.90 Ga) data are too sparse to make these calculations meaningful and velocity calculations are therefore restricted to data of 1.90 Ga and younger ages. The accumulated APW curve shows a number of linear segments with varying slopes, indicating sudden changes in drift rate. During the Middle Proterozoic (1.90−1.35 Ga) there was a period when the rate of APW was constant and low and that of latitudinal drift also was low. This pattern changed at ca. 1.35 Ga, and the following Middle-Late Proterozoic period can be described by rapid APW and strongly fluctuating drift velocities. Jotnian rifting and the intrusion of numerous dyke swarms (at ca. 1.25 Ga) correlate with this shift in rate. These changes are attributed to changes in plate configuration. A new database for the Ukrainian Shield is also presented, and GMPs in the 2.32−1.20 Ga range are defined. The database is still inadequate and the comparison of the Ukrainian and Fennoscandian drift histories is therefore tentative. Similarities in position, latitudinal drift and rotation during the Early-Middle Proterozoic are, nevertheless, evident. A close relationship between the shields in this period is consistent with the low APW rate of Fennoscandia, indicating that Fennoscandia may have been part of a larger continent, including the Ukraine, at that time. At ca. 1.2 Ga, the latitudinal position of Ukraine differed significantly from that of Fennoscandia, suggesting that the large shield split up between ca. 1.35 and 1.2 Ga. This would explain the change in APW rate at 1.35 Ga. The subsequent increase in rate was due to a reduction in the size of the shield. The discrepancy in palaeopositions of Fennoscandia and Ukraine at 1.2 Ga led Mikhailova and Kravchenko to suggest a late Precambrian time (1.07−0.57 Ga) for the accreation of Fennoscandia to the East European Platform (EEP). This may be correct as the rate of APW for Fennoscandia decreased in the late Precambrian, reflecting such a consolidation.

Tektites and climate

Only four tektite strewn fields have been produced during the past 40 m.y. even though at least 60 impact craters have been produced during the same period in continental lithologies having tektite‐like compositions. The apparent reason for this discrepancy is that the ejecta from most crater‐forming impacts was not completely melted. Laboratory and modeling studies show that projectiles as different as anorthosite and metal (densities from 2.8 to 8 g cm−3) produce similar amounts of melt, and this conclusion probably holds for comet‐like densities near 1.5 g cm−3. Our interpretation of the limited evidence indicates that the influence of projectile trajectory and velocity on melting efficiency is minor. The key factor affecting melt production seems to be the nature of the target, particularly its porosity; the fraction of projectile kinetic energy converted to heat may be an order of magnitude higher in a highly porous target than in a void‐free target. The grain size and water content of the target are also important. The ideal target is a porous, fine‐grained sediment such as loess, particularly if it is also dry. We suggest that the rate of impact production of fully molten crater ejecta is proportional to the fraction of the continental surface having thick (>10 m) blankets of dry loess and that tektites are mainly produced during cold, dry climate periods when such deposits are an order of magnitude more common than at present. This model is best tested at the Australasian site, since detailed climate records cannot be obtained for the Czechoslovakian and North American sites and have not yet been obtained for the Ivory Coast site. The fossil O isotopic records in cores containing the Australasian microtektites show that these were deposited during a period of cold climate near glacial stage 20.2. The chemical homogeneity and the high 10Be contents of Australasian tektites are well explained by melting a loess target.

Fossil pigments as indicators for palaeoclimatic interpretations —A case study of Qinghai Lake

An 82 cm core was collected from Qinghai Lake in the Qinghai-Xizang Plateau, China and sectioned in intervals of 1 cm for analysis of pigments (i. e. chlorophyll derivatives, carotenoids, myxoxanthophyll, oscillaxanthin) and210Pb.210Pb dating was used to establish the chronological sequence. The concentrations of myxoxanthophyll and oscillaxanthin from the cyanophytes increase with temperature. There are four peak values at 0–14 cm (present−1891a), 25 cm (1786a), 45 cm (1581a), 60 cm (1416a) representing four warm and low water level periods during the past 700 years. This was confirmed by the high concentration of carbonate and ∂13C in these stages. In these 700 years, there were also 4 periods of cold wet climate and high water level as indicated by the tree ring index and high value of native chlorophyll and high, variable CD/TC ratios.

Relationship between climatic change and the nomadic southward migrations in eastern Asia during historical times

On the basis of data obtained from ancient Chinese chronicles, this study has established time series of southward and eastward migrations of the nomad people in the southern Mongolian grasslands and eastern central Asia from 190 B.C. to A.D. 1880 and found that there is a close relationship between climatic change and the migrations. We hypothesized that such a climate-migration relationship perhaps resulted from both livestock failure of the nomad people and crop failure of the Han Chinese during cold and/or dry climatic periods.

A revision of Afrotropical Agabus Leach (Coleoptera, Dytiscidae), and the evolution of tropicoalpine super specialists

Abstract. The thirteen species of Agabus Leach, 1817, of the Afrotropical Region are revised and classified into four species groups: the dibasic ambulator-group endemic to Ethiopia, ragazzii-group with five species in Ethiopia, raffrayi-group with five species in East and South Africa, and A.discicollis Ancey, 1882, endemic to Ethiopia, is placed in the Nearctic cordatus-group. Agabus perssoni sp.n. and Agabus galamensis sp.n. are described from the highlands of Ethiopia. Agabus ruwenzoricus Guignot, 1936, stat.n. is given specific rank. Agabus ferrugatus Régimbart, 1905, is synonymized with Agabus ragazzii Régimbart, 1887, and Agabus limbicollis Régimbart, 1905, is synonymized with Agabus raffrayi Sharp, 1882, syn.n. Lectotypes are designated for the following nominal species: Agabus discicollis Ancey, 1882, Agabus raffrayi Sharp, 1882, Agabus limbicollis Régimbart, 1905, Agabus pallidus Omer-Cooper, 1931, Agabus ruwenzoricus Guignot, 1936, Agabus sjostedti Régimbart, 1908, Agabus dytiscoides Régimbart, 1908, Agabus ragazzii Régimbart, 1887, Agabus ferrugatus Régimbart, 1905, and Gaurodytes abessinicus Zimmermann, 1928. Reconstructed phylogenies are presented for the raffrayi-and ragazzii-groups. The following adaptations to tropicoalpine habitats are suggested: (1) body and especially pronotum narrow, (2) head broad anteriorly, (3) hindwing small, and (4) hind leg long and slender. Biogeography and evolution of the studied species are discussed. Four different invasions of Holarctic lineages to the East African mountains are suggested. Recurrent periods of cold and dry climate are considered the chief driving force in the evolution of high altitude super specialists.

A model of late quaternary landscape development in the Delaware Valley, New Jersey and Pennsylvania

In the Delaware Valley of New Jersey and eastern Pennsylvania the late Quaternary history of colluviation, fluvial adjustment, and soil formation is based on the ages of pre-Wisconsinan soils and glacial deposits which are indicated by feld relationships and inferred from mid-latitude climate changes indicated by marine oxygen-isotope records. The area is divided into four terranes characterized by sandstone, gneiss, slate and carbonate rocks. Since the last pre-Wisconsinan glaciation (> 130 ka, inferred to be late Illinoian), each terrane responded differently to chemical and mechanical weathering. During the Sangamon interglacial stage (∼ 130-75 ka) in situ weathering is inferred to have occurred at rates greater than transportation of material which resulted in the formation of deep, highly weathered soil and saprolite, and dissolution of carbonate rocks. Cold climatic conditions during the Wisconsinan, on the other hand, induced erosion of the landscape at rates faster than soil development. Upland erosion during the Wisconsinan removed pre-Wisconsinan soil and glacial sediment and bedrock to produce muddy to blocky colluvium, grézes litées, and alluvial fans on footslopes. Fluvial gravel and overlying colluvium in the Delaware Valley, both buried by late Wisconsinan outwash, are inferred to represent episodes of early and middle Wisconsinan (∼ 75-25 ka) upland erosion and river aggradiation followed by river degradation and colluvium deposition. Early-middle Wisconsinan colluvium is more voluminous than later colluvium despite colder, possibly permafrost conditions during the late Wisconsinan ∼ 25-10 ka). Extensive colluviation during the early and middle Wisconsinan resulted from a longer (50 kyr), generally cold interval of erosion with a greater availability of easily eroded pre-Wisconsinan surficial materials on uplands than during the late Wisconsinan. After recession of late Wisconsinan ice from its terminal position, soil formation and landscape stability were delayed until the Holocene by a lingering cold climate, slope erosion, colluvium and alluvial fan deposition, and eolian sedimentation. Late Quaternary erosion in the Delaware Valley was dominated by glacial and periglacial processes during glacial stages. During the warm interglacial stages, soils developed on a more stable landscape. These souls were easily colluviated by periglacial erosion during periods of intermittent cold climate.

The Dilemma of the Rapid Variations in CO2 in Greenland Ice Cores (Abstract)

The Dilemma of the Rapid Variations in CO₂ in Greenland Ice Cores (Abstract)

The Dilemma of the Rapid Variations in CO2 in Greenland Ice Cores (Abstract)

The Dilemma of the Rapid Variations in CO2 in Greenland Ice Cores (Abstract)

Ecological adaptation of reproduction in Northeast Arctic cod

A recent period (1977–1982) of cold climate in the Barents Sea resulted in a greatly reduced feeding area available for the Arctic cod and in consistently low recruitment. With the start of a warmer period in 1982/83, the area and potential for production of cod biomass expanded and recruitment has increased. A hypothesis is presented that through evolutionary processes, the reproduction of the Arctic cod is adjusted to the variations in the feeding area caused by climatic fluctuations. Historical data on sea temperature and ice cover are used to describe the climatic fluctuations for the period 1900–1983 and these are compared with data on fluctuations in year-class strength. It is concluded that conditions favouring high survival rates of cod larvae must be related to the occurrence of high temperatures in the Atlantic component of the Norwegian current. The processes and/or phenomena must have a large time and space scale. This is also confirmed by the high incidence of temporal similarity in survival success of the stocks of cod, haddock and herring in this area.

Gentle Slopes and Fluvial Terraces around Mt. Shokanbetsudake, Hokkaido

This paper discusses the paleoenvironment of eastern slopes of Mt. Shokanbetsudake, Hokkaido, on the basis of evidences of gentle slopes and fluvial terraces.The fluvial terraces are classified into five surfaces (terrace I to V in descending order) and the gentle slopes into two surfaces (gentle slope I and II). In most case, gentle slope I and gentle slope II develop behind terrace II and behind terrace IV, respectively.The gentle slopes are mainly composed of lower angular gravel several meters thick and upper fine textured materials several meters thick, which were produced by reworking of the lower layer. Long axis direction of the angular gravel is consistent with the maximum slope direction. The facts indicate that the gentle slopes were developed by gelifiuction under a periglacial environment.The age of gentle slope I formation is estimated to be older than 40, 000 or 40, 000-20, 000yr B. P. as inferred by the C-14 ages of peat and charcoal buried in the deposits of gentle slope I and terrace III. Terrace II and III are considered to have developed in this period, and the feature of their deposits suggests that they were formed under a colder climatic environment than present.On the other hand, the gentle slope II is inferred to have developed in a short period of cold climate between 20, 000yr B. P. and 5, 000yr B. P.

Glaciations in the United Kingdom

The basic objective of Project 24 was correlation of glaciations. This inevitably involves consideration also of interglacials and interstadials, as well as periods of cold climate shown by biological indicators or by oxygen isotope ratios in deep sea cores but not cold enough to generate glaciers in this country. Before giving conclusions about correlation which have been reached during the last 8-9 years, it is important to summarise what progress has been made in absolute dating which, if reliable, is the best tool for correlation.

Interregional correlation of benthic foraminiferal faunas along the northeast pacific margin—climatic controls

Similarity of benthic foraminiferal faunas from the Gulf of Alaska Tertiary Province and central California fluctuates during the middle Cenozoic, being highest (most similar) in the late Eocene and again in the early Miocene. A major lineage of benthic foraminifera, the uvigerinid—siphogenerinid, extends its range northward into the Gulf of Alaska at these times. These relationships can be correlated to climatic fluctuations as defined by oxygen isotopic analysis. Increased faunal cosmopolitanism during warm climatic periods increases the geographic extent to which benthic foraminiferal correlations can be made. During cold climatic periods faunal endemism increases and correlations become more difficult or impossible. Consideration of the effects of climate on faunal distributions, combined with detailed analysis of local paleoenvironmental influences, provides a basis for better evaluating both interbasinal and interregional foraminiferal correlations.

Periglacialmorfologisk forskning i de nordiska länderna

Svensson, Harald. Periglacial research in the Norden countries. Geografisk Tidsskrift 82: 25–29. Copenhagen, November 1982. For studies of frozen-ground morphology Norden is an area of great interest due to the intense frost processes acting in the north and traces of frozen-ground features from former periods of cold climate in the southern parts.

Contamination of the Lake Tahoe Air Basin by High Molecular Weight Petroleum Residues

The atmosphere of the Lake Tahoe air basin is contaminated with high molecular weight (> C12) petroleum hydrocarbons. Aerosol samples were collected by high-volume filtration and the solvent-soluble organic matter was analyzed. The relative concentrations of petroleum residues found were as follows: winter > summer and day > night. This contamination is primarily due to the poorer combustion of diesel and home heating fuels at that altitude and during periods of colder climate.

Terrasses et phenomenes periglaciaires dans la vallee de l'Huisne en amont du Mans (Sarthe)

Abstract Describes the succession of terraces in the Huisne valley above Le Mans, Sarthe, France, and discusses the effects of solifluction and other periglacial processes, the accumulation of eolian material, and the morphologic development of the terraces. It is concluded that the terraces represent climatically controlled (rather than eustatic) land forms and that there were periods of coldclimate in western France prior to the Wuerm glaciation.

Some Periglacial Features in Central Montana

Two types of structures represent the results of former intensive frost action in central Montana. Involutions, which consist of local deformation and interpenetration in stratified materials, are common throughout the area and occur in a variety of forms. They are believed to have developed by differential freezing and growth of ground-ice, in a seasonally thawed zone overlying perennially frozen ground. Wedge structures, found at a few localities, consist of wedge-shaped vertical fissures in weathered bedrock. The fissures form polygonal networks and have been filled by slumping of surface materials. They are believed to have been opened by ice veins developed when the ground became perennially frozen. A mean annual temperature at least 8° C. below that of the present would be required for the development of perennially frozen ground. This period of colder climate probably occurred at the time of the last glaciation of adjoining areas, which may belong to the Middle Wisconsin substage.