Interacting Loop Current variability and Mississippi River discharge over the past 400 kyr

Nürnberg, Dirk; Ziegler, Martin; Karas, Cyrus; Tiedemann, Ralf; Schmidt, M. W.

doi:10.1016/j.epsl.2008.04.051

Cited by 84 publications

(122 citation statements)

References 72 publications

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“…a positive interaction of an intensified LC and wind systems favouring Ekman transport of subsurface waters onto the shelf and into the shallow water zone (Fernald and Purdum, 1981;Li and Weisberg, 1999). This inference is in agreement with notions of an intensified LC during interglacials (Nürnberg et al, 2008). The high sea levels during interglacials may have further promoted intrusions of nutrient-rich water masses in the shallow water zone.…”

Section: Upwelling As a Driver Of High Skeletal Productivity?supporting

confidence: 76%

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

et al. 2016

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Abstract. The fast growing calcareous skeletons of zooxanthellate reef corals (z corals) represent unique environmental proxy archives through their oxygen and carbon stable isotope composition (δ 18 O, δ 13 C). In addition, the accretion of the skeleton itself is ultimately linked to the environment and responds with variable growth rates (extension rate) and density to environmental changes. Here we present classical proxy data (δ 18 O, δ 13 C) in combination with calcification records from 15 massive z corals. The z corals were sampled from four interglacial units of the Florida carbonate platform (USA) dated approximately 3.2, 2.9, 1.8 and 1.2 Ma (middle Pliocene to early Pleistocene). The z corals (Solenastrea, Orbicella, Porites) derive from unlithified shallow marine carbonates and were carefully screened for primary preservation suited for proxy analysis. We show that skeletal accretion responded with decreasing overall calcification rates (decreasing extension rate but increasing density) to warmer water temperatures. Under high annual water temperatures, inferred from sub-annually resolved δ 18 O data, skeletal bulk density was high, but extension rates and overall calcification rates were at a minimum (endmember scenario 1). Maximum skeletal density was reached during the summer season giving rise to a growth band of high density within the annually banded skeletons ("high density band", HDB). With low mean annual water temperatures (endmember scenario 2), bulk skeletal density was low but extension rates and calcification rates reached a maximum, and under these conditions the HDB formed during winter. Although surface water temperatures in the Western Atlantic warm pool during the interglacials of the late Neogene were ∼ 2 • C higher than they are in the present day, intermittent upwelling of cool, nutrient-rich water mitigated water temperatures off southwestern Florida and created temporary refuges for z coral growth. Based on the sub-annually resolved δ 18 O and δ 13 C records, the duration of the upwelling episodes causing the endmember 2 conditions was variable and lasted from a few years to a number of decades. The episodes of upwelling were interrupted by phases without upwelling (endmember 1) which lasted for at least a few years and led to high surface water temperatures. This variable environment is likely one of the reasons why the coral fauna is dominated by the eurytopic genus Solenastrea, also a genus resistant to high turbidity. Over a period of ∼ 50 years, the oldest sub annually resolved proxy record available (3.2 Ma) documents a persistent occurrence of the HDB during winter. In contrast, the HDB forms in summer in modern z corals from the Florida reef tract. We suggest this difference should be tested as being the expression of a tendency towards decreasing interglacial upwelling since the middle Pliocene. The number of z coral sclerochronological records for the Plio-Pleistocene is still rather low, however, and requires more data and an improved resolution, through records from...

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Section: Upwelling As a Driver Of High Skeletal Productivity?supporting

confidence: 76%

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

et al. 2016

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“…The increase in Hadley circulation possibly led to an increase in easterly trade winds over the western equatorial North Atlantic in summer (Zhang and Delworth 2005), thereby enhancing Loop Current intrusion into the GoM and warming the surface waters around the Florida peninsula. The observed increase of summer precipitation and November temperature in Florida could therefore represent an increase in summer trade winds and reflect the persistence of the AWP and increased Loop Current during North Atlantic cold spells (Nürnberg et al 2008;Ziegler et al 2008). It contrasts the presumed same-sign synchronicity of low and high latitude climates during the late Glacial as observed in a planktic foraminiferal Mg/Ca record from the Cariaco Basin on the northern Venezuelan shelf (Lea et al 2003).…”

Section: Source Of Heat and Moisture Anomaliesmentioning

confidence: 79%

“…Heinrich event ages, and hence the Lake Tulane record below TP4, have been updated to the new Greenland Ice Core Chronology 2005 (GICC05), which is based on layer counting of the NGRIP ice core back to 60 ka Svensson et al 2008) Hodell et al (1991) and Poore et al (2004) indicate that during the Holocene the Loop Current was mainly controlled by the effect of summer insolation on ITCZ position. Nürnberg et al (2008) reconstructed SSTs and sea surface salinities in the northeastern GoM (Florida margin) over the past 400 kyr. Their results reveal that Loop Current intrusion was modulated by the northward extend of the AWP and freshwater discharge from the Laurentide Ice Sheet.…”

Section: Source Of Heat and Moisture Anomaliesmentioning

confidence: 99%

Impact of the Atlantic Warm Pool on precipitation and temperature in Florida during North Atlantic cold spells

et al. 2009

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Recurrent phases of increased pine at Lake Tulane, Florida have previously been related to strong stadials terminated by so-called Heinrich events. The climatic significance of these pine phases has been interpreted in different ways. Using a pollen-climate inference model, we quantified the climate changes and consistently found that mean summer precipitation (P JJA ) increased (0.5-0.9 mm/day) and mean November temperature increased (2.0-3.0°C) during pine phases coeval with Heinrich events and the Younger Dryas. Marine sea surface temperature records indicate that potential sources for these moisture and heat anomalies are in the Gulf of Mexico and the western tropical Atlantic. We explain this low latitude warming by an increased Loop Current facilitated by persistence of the Atlantic Warm Pool during summer. This hypothesis is supported by a climate model sensitivity analysis. A positive heat anomaly in the Gulf of Mexico and equatorial Atlantic best approximates the polleninferred climate reconstructions from Lake Tulane during the (stadials around) Heinrich events and the Younger Dryas.

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“…While alkenone- derived SST records indicate a warming over the Holocene, Mg/Caderived SST records indicate either no trend or a cooling trend for the same time period. In particular, the cooling trend as recorded in the Mg/Ca-derived SST record off of the Mississippi River mouth has been assumed to reflect a summer temperature signal (Nü rnberg et al, 2008). Unpublished alkenone results from the same core indicate a warming (Nü rnberg and Blanz, personal communication), suggesting a winter-weighted temperature record if the concept of seasonal insolation changes shaping SST records in a different manner as discussed for the EEP are applied to the WEA.…”

Section: Mg/ca-derived Sst Trends During the Holocenementioning

confidence: 99%

Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry

Leduc

Schneider

Kim

et al. 2010

Quaternary Science Reviews

385

238

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a b s t r a c tIn this study we review a global set of alkenone-and foraminiferal Mg/Ca-derived sea surface temperatures (SST) records from the Holocene and compare them with a suite of published Eemian SST records based on the same approach. For the Holocene, the alkenone SST records belong to the actualized GHOST database (Kim, J.-H., Schneider R.R., (2004). GHOST global database for alkenone-derived Holocene seasurface temperature records. Available from: http://www.pangaea.de/Projects/GHOST.), while the Mg/ Ca-derived SST database represents a new compilation. The actualized GHOST database not only confirms the SST changes previously described but also documents the Holocene temperature evolution in new oceanic regions such as the Northwestern Atlantic, the eastern equatorial Pacific, and the Southern Ocean. A comparison of Holocene SST records stemming from the two commonly applied paleothermometry methods reveals contrasting -sometimes divergent -SST evolution, particularly at low latitudes where SST records are abundant enough to infer systematic discrepancies at a regional scale. Opposite SST trends at particular locations could be explained by out-of-phase trends in seasonal insolation during the Holocene. This hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms. As a simple test for this hypothesis, Eemian SST records are considered because the Holocene and Eemian time periods experienced comparable changes in orbital configurations, but had a higher magnitude in insolation variance during the Eemian. For several regions, SST changes during both interglacials were of a similar sign, but with higher magnitudes during the Eemian as compared to the Holocene. This observation suggests that the ecological mechanism shaping SST trends during the Holocene was comparable during the penultimate interglacial period. Although this ''ecology hypothesis'' fails to explain all of the available results, we argue that any other mechanism would fail to satisfactorily explain the observed SST discrepancies among proxies.

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Interacting Loop Current variability and Mississippi River discharge over the past 400 kyr

Cited by 84 publications

References 72 publications

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

Upwellings mitigated Plio-Pleistocene heat stress for reef corals on the Florida platform (USA)

Impact of the Atlantic Warm Pool on precipitation and temperature in Florida during North Atlantic cold spells

Holocene and Eemian sea surface temperature trends as revealed by alkenone and Mg/Ca paleothermometry

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