Paleoenvironmental history of the Chilean Fjord region and the adjacent southeast Pacific over the last 60 kyr BP: A multiproxy analysis on high resolution sediment cores

The Chilean Fjord region offers a unique opportunity to study past ocenographic and environmental changes as it is the only land mass in the Southern Hemisphere intercepting the Southern Westerly Winds (SWW) which are of global importance. Three sediment cores from the Chilean Fjord Region and the adjacent southeast Pacific were used to study past sea surface temperature variations and their relationship to climate changes during most of the last glacial period and the Holocene. Core MD07-3128 was recovered at 53°S at the Pacific entrance of the Strait of Magellan. Carbon-14 ages and paleomagnetic chronology indicate that core MD07-3128 covers the last 60 kyr BP. Its high-sedimentation rates allow to depict millennial-scale sea surface temperature (SST) and paleoproductivity changes over the last 60 kyr BP. Cores MD07-3124 and JPC-42, on the other hand, were recovered at 51°S and 50°S, from Canal Concepción and Canal Wide, respectively. These cores were used to reconstruct the first continuos SST records over the entire Holocene. Alkenone-derived SST data from the southernmost record MD07-3128 (53°S) show that glacial temperatures were ca. 7°C colder than early Holocene SST values. Substantial millennial-scale variability of 2-3°C characterized the last glacial period, while a very strong warming of 7°C was recorded over the last deglaciation. A cooling trend culminating during the Last Glacial Maximum (LGM) has been recorded. This regional cooling has been related to the proximal location of the core site to the large Patagonian Ice Sheet (PIS) and related melt-water supply, at least during the LGM. An increase in the relatively abundances of C37:4 alkenones, a proxy for low salinity waters, support the idea of large meltwater input during this time interval. On millennial-time scales, changes in marine plankton productivity were also recorded. An increase in the siliceous plankton community over the calcareous characterized the colder intervals while during the warmer ones this pattern was reversed. These marine productivity changes can be associated with a northward shift of the Southern Ocean fronts and the opal belt during glacial cold periods and/or changes in the nutrient advection consistent with our lower planktonic foraminiferal d13C data. Interestingly, the siliceous community was comparatively lower around the LGM suggesting a reduced biological productivity probably due to enhanced meltwater input from the large PIS resulting in high surface water stratification. During the Holocene, cores JPC-42 and MD07-3124 show no evidence for an early Holocene climate optimum as previously described for the Chilean continental margin furthern north. In constrast, SST were warmer than present during most of the Holocene except for the prominent cooling centered at 5 kyr BP and the cooling trend recorded in the latest Holocene. the absence of an early Holocene warm phase in the inner fjord has been associated with a combination of factors including inflow of open marine waters due to lower sea-level, enhanced advection of colder and fresher inner fjord water, stronger westerly winds, and reduced local summer insolation. The fact that alkenones in the inner fjord core JPC-42 (located near to the southern Patagonian icefield) were only present after 8 kyr BP point to susbtantially reduced surface water salinities during the early Holocene, strongly consistent with increasinng precipitation and runoff in the core of the SWW

Paläoumweltgeschichte der chilenischen Fjordregion und des benachbarten Südostpazifiks während der letzten 60000 Jahre: Eine Multiproxy-Studie an höchstauflösenden Sedimentkernen

The Chilean Fjord region offers a unique opportunity to study past ocenographic and environmental changes as it is the only land mass in the Southern Hemisphere intercepting the Southern Westerly Winds (SWW) which are of global importance. Three sediment cores from the Chilean Fjord Region and the adjacent southeast Pacific were used to study past sea surface temperature variations and their relationship to climate changes during most of the last glacial period and the Holocene. Core MD07-3128 was recovered at 53°S at the Pacific entrance of the Strait of Magellan. Carbon-14 ages and paleomagnetic chronology indicate that core MD07-3128 covers the last 60 kyr BP. Its high-sedimentation rates allow to depict millennial-scale sea surface temperature (SST) and paleoproductivity changes over the last 60 kyr BP. Cores MD07-3124 and JPC-42, on the other hand, were recovered at 51°S and 50°S, from Canal Concepción and Canal Wide, respectively. These cores were used to reconstruct the first continuos SST records over the entire Holocene. Alkenone-derived SST data from the southernmost record MD07-3128 (53°S) show that glacial temperatures were ca. 7°C colder than early Holocene SST values. Substantial millennial-scale variability of 2-3°C characterized the last glacial period, while a very strong warming of 7°C was recorded over the last deglaciation. A cooling trend culminating during the Last Glacial Maximum (LGM) has been recorded. This regional cooling has been related to the proximal location of the core site to the large Patagonian Ice Sheet (PIS) and related melt-water supply, at least during the LGM. An increase in the relatively abundances of C37:4 alkenones, a proxy for low salinity waters, support the idea of large meltwater input during this time interval. On millennial-time scales, changes in marine plankton productivity were also recorded. An increase in the siliceous plankton community over the calcareous characterized the colder intervals while during the warmer ones this pattern was reversed. These marine productivity changes can be associated with a northward shift of the Southern Ocean fronts and the opal belt during glacial cold periods and/or changes in the nutrient advection consistent with our lower planktonic foraminiferal d13C data. Interestingly, the siliceous community was comparatively lower around the LGM suggesting a reduced biological productivity probably due to enhanced meltwater input from the large PIS resulting in high surface water stratification. During the Holocene, cores JPC-42 and MD07-3124 show no evidence for an early Holocene climate optimum as previously described for the Chilean continental margin furthern north. In constrast, SST were warmer than present during most of the Holocene except for the prominent cooling centered at 5 kyr BP and the cooling trend recorded in the latest Holocene. the absence of an early Holocene warm phase in the inner fjord has been associated with a combination of factors including inflow of open marine waters due to lower sea-level, enhanced advection of colder and fresher inner fjord water, stronger westerly winds, and reduced local summer insolation. The fact that alkenones in the inner fjord core JPC-42 (located near to the southern Patagonian icefield) were only present after 8 kyr BP point to susbtantially reduced surface water salinities during the early Holocene, strongly consistent with increasinng precipitation and runoff in the core of the SWW

cKd-tree: A Compact Kd-tree

In the context of Big Data scenarios, the presence of extensive static datasets is not uncommon. To facilitate efficient queries on such datasets, the utilization of multiple indexes, such as the Kd-tree, becomes imperative. The current scale of managed points may, however, exceed the capacity of primary memory, posing a significant challenge. In this article we introduce cKd-tree, a compact data structure designed to represent a Kd-tree efficiently. The structure cKd-tree is essentially an encoding of the spiral code sequence of points within an implicit Kd-tree (iKd-tree) using Directly Addressable Codes (DACs). The unique feature of cKd-tree lies in its ability to perform spiral encoding and decoding of points by relying solely on knowledge of their parent points within the iKd-tree. This inherent property, combined with DACs’ direct access capability to sequence elements, enables cKd-tree to traverse and explore the tree while decoding only the nodes relevant to queries. The article details the algorithms necessary for creating and manipulating a cKd-tree, as well as algorithms for evaluating two fundamental queries over points: the point query and the range query. To assess the performance of cKd-tree, a series of experiments are conducted, comparing it with iKd-tree and $k^{2}$ -tree data structures. The evaluation metrics include compression efficiency and execution time of queries. cKd-tree achieves a compression ratio comparable to that of $k^{2}$ -tree, approximately 70%, demonstrating heightened efficiency, particularly in scenarios characterized by sparse data. Additionally, consistent with expectations, $k^{2}$ -tree exhibits superior performance in querying individual points, whereas cKd-tree outperforms in the context of aggregate data queries, such as range queries

Optimizing repair programs for consistent query answering

Databases may not satisfy integrity constraints (ICs) for several reasons. Nevertheless, in most of the cases an important part of the data is still consistent wrt certain desired ICs, and the database can still give some correct answers to queries wrt those ICs. Consistent query answers are characterized as ordinary answers obtained from every minimally repaired and consistent version of the database. Database repairs can be specified as stable models of disjunctive logic programs with program constraints. In this paper, we optimize repair programs, model computation, and query evaluation from them. We make repair programs more compact by eliminating redundant rules and unnecessary programs denial constraints. These results facilitate the application of magic sets techniques to query evaluation in general, and in DLV, a logic programming system that implements the stable models semantics, in particular. We also analyze the implementation in DLV of queries with aggregate functions