scholarly journals North Pacific-wide spreading of isotopically heavy nitrogen during the last deglaciation: Evidence from the western Pacific

2008 ◽  
Vol 5 (6) ◽  
pp. 1641-1650 ◽  
Author(s):  
S. J. Kao ◽  
K. K. Liu ◽  
S. C. Hsu ◽  
Y. P. Chang ◽  
M. H. Dai
Keyword(s):  
North Pacific ◽  
Accumulation Rate ◽  
Okinawa Trough ◽  
Last Deglaciation ◽  
The Okinawa Trough ◽  
A Site ◽  
Two Peaks ◽  
Heavy Nitrogen ◽  
The Last Glacial Maximum ◽  
The Last Glacial

Abstract. Sedimentary δ15 N records in two IMAGES cores (MD012404 and MD012403) retrieved from the Okinawa Trough (OT) in the western North Pacific reveal deglacial increases with two peaks occurring during the Bølling/Allerød and the Preboreal/early Holocene periods. These peaks are synchronous with previously reported δ15 N peaks in the Eastern Tropical North Pacific, although the amplitudes (from 3.8 to 5.8‰) are much smaller in the OT. Similar δ15 N values for the last glacial maximum and the late-Holocene observed by us at a site far from the present-day zones of water-column denitrification (WCD) indicate that the mean 15 N/14 N of nitrate in the upper ocean did not differ much between the two climate states. The accumulation rate of organic carbon and total sulfur content are used as indices of the local WCD potential. The results suggest that enhancement of global WCD rather than local denitrification should be responsible for the deglacial maxima of sedimentary δ15 N in the Okinawa Trough. Our data could provide additional constraints to better understand changes in nitrogen budget during the glacial to interglacial transition.

scholarly journals North Pacific-wide spreading of isotopically heavy nitrogen from intensified denitrification during the Bølling/Allerød and post-younger dryas periods: evidence from the Western Pacific

2008 ◽  
Vol 5 (2) ◽  
pp. 1017-1033 ◽  
Author(s):  
S. J. Kao ◽  
K. K. Liu ◽  
S. C. Hsu ◽  
Y. P. Chang ◽  
M. H. Dai
Keyword(s):  
North Pacific ◽  
Okinawa Trough ◽  
Younger Dryas ◽  
The Past ◽  
The Okinawa Trough ◽  
The Mean ◽  
The Kuroshio ◽  
Heavy Nitrogen ◽  
Critical Constraints ◽  
The Western Pacific

Abstract. Sedimentary δ15N record for the past 30 ka buried in the Okinawa Trough in the western North Pacific mimicking the pattern from the Eastern Tropical North Pacific (ETNP), but the values (4.4–5.8‰) and the amplitude of the variation were much smaller than those (9–17‰) of the previous site. All but three values in the record were lower than the mean δ15N (5.6‰) of nitrate in the upper 800 m of the Kuroshio water suggesting additional inputs of isotopically light nitrogen from N2-fixation. The peak values of δ15N occurred during the Bølling/Allerød period and the warming period right after the Younger Dryas, synchronous to those found in the Eastern North Pacific. It is highly probable the high δ15N values are originated from the influence of the intensified denitrification in the ETNP during the warming periods. These new data represent the sedimentary record most distant from the intensive denitrifying zone in the ETNP and may serve as critical constraints to better quantify the nitrogen budget in the last climate cycle.

A biomarker record of temperature and phytoplankton community structure in the Okinawa Trough since the last glacial maximum

2017 ◽  
Vol 88 (1) ◽  
pp. 89-97 ◽  
Author(s):  
Jiaping Ruan ◽  
Yunping Xu ◽  
Su Ding ◽  
Yinghui Wang ◽  
Xinyu Zhang
Keyword(s):  
Phytoplankton Community ◽  
Okinawa Trough ◽  
Kuroshio Current ◽  
Community Change ◽  
Community Structures ◽  
Ocean Drilling Program ◽  
The Holocene ◽  
The Okinawa Trough ◽  
The Kuroshio ◽  
The Last Glacial

AbstractA variety of biomarkers were examined from Ocean Drilling Program Core 1202B to reconstruct temperature and phytoplankton community structures in the southern Okinawa Trough since 20 ka. Two molecular temperature proxies ( $${\rm U}_{{37}}^{{{\rm K}\prime}} $$ and TEX86) show 5°C to ~6°C warming during the glacial-interglacial transition. Prior to the Holocene, the $${\rm U}_{{37}}^{{{\rm K}\prime}} $$ -derived temperature was generally 1°C to 4°C higher than TEX86-derived temperature. This difference, however, was reduced to <1°C in the Holocene. Correspondingly, the phytoplankton biomarkers (e.g., C37:2 alkenone, brassicasterol, C30 1,15 diol, and dinosterol) indicate a shift of planktonic community structures, with coccolithophorids becoming more abundant in the Holocene at the expense of diatoms/dinoflagellates. This shift is related to the variability of nutrients, temperature, and salinity in the Okinawa Trough, likely controlled by the sea level and the intensity of the Kuroshio Current. The phytoplankton community change may have had profound implications for atmospheric CO2 fluctuations during glacial-interglacial cycles since diatoms and dinoflagellates have a higher efficiency of the biological pump than coccolithophorids.

Vegetation Dynamics During the Last Deglaciation, Southeastern Great Basin, U.S.A.

1990 ◽  
Vol 33 (2) ◽  
pp. 188-203 ◽  
Author(s):  
W. Geoffrey Spaulding
Keyword(s):  
Great Basin ◽  
Vegetation Change ◽  
Last Deglaciation ◽  
Arrival Times ◽  
Last Glacial ◽  
Local Extinctions ◽  
Dispersal Distances ◽  
Almost All ◽  
A Site ◽  
The Last Glacial

AbstractVegetation changes in the southeastern Great Basin between 17,500 and 8000 yr B.P. can be reconstructed from plant macrofossil assemblages in ancient packrat (Neotoma spp.) middens. Vegetation instability after ca. 16,000 yr B.P. involved a dispoportionate number of local immigrations (arrivals) relative to apparent local extinctions (departures). At a site in modern woodland, less than 50% of the arrivals were of transients, species that subsequently went locally extinct; but at a low-elevation desert site almost all arrivals before 10,000 yr B.P. were transient species. Thus, by the close of the last glacial age, higher elevations supported vegetation that resembled present woodland, while lower elevations supported desertscrub that bore little resemblance to modern thermophilous desertscrub.Differences in the pace of plant community “modernization” in different elevational zones can be attributed to migrational lag. Woodland species survived the last glacial age at low elevations nearby, and began arriving at sites within current woodland before 11,700 yr B.P. Warm-desert plants were displaced far to the south, and began arriving after 9500 yr B.P. Moreover, their staggered arrival times suggest that low winter temperatures did not inhibit their migration during the early Holocene. These data suggest that biotic factors, particularly variable dispersal distances and consequent migrational lag, did affect deglacial vegetation change.

Sediment record of precipitation and changes in circulation in Bohol Sea area since the Last Glacial Maximum

2020 ◽  
Author(s):  
Sarahmae Buen ◽  
Fernando Siringan ◽  
Ronald Lloren
Keyword(s):  
Sea Level ◽  
Last Glacial Maximum ◽  
Accumulation Rate ◽  
The Philippines ◽  
Glacial Maximum ◽  
Radiocarbon Dates ◽  
Last Glacial ◽  
Sediment Input ◽  
The Last Glacial Maximum ◽  
The Last Glacial

&lt;p&gt;Deep marine sediments may provide insights of past climate and oceanographic events. Knowledge of the past events can aid in scenario setting of future climate and their oceanographic consequences. A deep sea sediment core from the western side of Bohol Sea, a marginal sea located south of the Philippines, was used to reconstruct precipitation and identify the impacts of sea level rise on the circulation of Bohol Sea.&amp;#160; Five radiocarbon dates from bulk organic matter provide age control spanning back to the Last Glacial Maximum. Sedimentological (lithics and carbonate fractions; bulk density; sedimentation rate and mass accumulation rate) and geochemical (Ti, Al, Zr, Ti/Al and Y/Ni) data were used to reconstruct the sediment input for the area. Sediment input was decreasing from 20-15ka, followed by a relatively stable trend until ~9ka. After ~9ka sediment input increased up until the most recent years. Sedimentation trend follows the average winter (DJF) insolation curve at 10&lt;sup&gt;o&lt;/sup&gt;N. This signifies that the sediment input reflects the general changes in precipitation in the area. Lithics and carbonate contents reflect a shift in sediment source that could be attributed to the change in circulation in the basin as the sea level rose to overtop the Surigao Strait located at the northeastern side of the basin. Greater westward transport of suspended material from large rivers to the east would contribute to the sedimentation in the western part of Bohol Sea.&lt;/p&gt;

A 110,000-Yr Record of Explosive Volcanism from the GISP2 (Greenland) Ice Core

1996 ◽  
Vol 45 (2) ◽  
pp. 109-118 ◽  
Author(s):  
Gregory A. Zielinski ◽  
Paul A. Mayewski ◽  
L. David Meeker ◽  
S. Whitlow ◽  
Mark S. Twickler
Keyword(s):  
Ice Core ◽  
Explosive Volcanism ◽  
Climate Forcing ◽  
Last Deglaciation ◽  
The Past ◽  
Or Groups ◽  
Circulation Patterns ◽  
Second Period ◽  
The Last Glacial Maximum ◽  
The Last Glacial

AbstractThe time series of volcanically produced sulfate from the GISP2 ice core is used to develop a continuous record of explosive volcanism over the past 110,000 yr. We identified ∼850 volcanic signals (700 of these from 110,000 to 9000 yr ago) with sulfate concentrations greater than that associated with historical eruptions from either equatorial or mid-latitude regions that are known to have perturbed global or Northern Hemisphere climate, respectively. This number is a minimum because decreasing sampling resolution with depth, source volcano location, variable circulation patterns at the time of the eruption, and post-depositional modification of the signal can result in an incomplete record. The largest and most abundant volcanic signals over the past 110,000 yr, even after accounting for lower sampling resolution in the earlier part of the record, occur between 17,000 and 6000 yr ago, during and following the last deglaciation. A second period of enhanced volcanism occurs 35,000–22,000 yr ago, leading up to and during the last glacial maximum. These findings further support a possible climate-forcing component in volcanism. Increased volcanism often occurs during stadial/interstadial transitions within the last glaciation, but this is not consistent over the entire cycle. Ages for some of the largest known eruptions 100,000–9000 yr ago closely correspond to individual sulfate peaks or groups of peaks in our record.

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