Geology topics

Jessica W. Spear

Publications and source records attributed to Jessica W. Spear.

6 recordsLinked to original sources

USGS2013

Seasonal flux and assemblage composition of planktic foraminifers from a sediment-trap study in the northern Gulf of Mexico

Sediment-trap samples from the northern Gulf of Mexico reveal that Globorotalia truncatulinoides, Neogloboquadrina dutertrei, Pulleniatina spp. (includes P. obliquiloculata and P. finalis), and the Globorotalia menardii group (includes Gt. menardii, Gt. tumida, and Gt. ungulata) generally occur in cold months. Globigerinoides ruber (white and pink varieties) and Globigennoides sacculifer occur throughout the year. The seasonal occurrence of individual taxa of planktic foraminifers in the Gulf of Mexico have important differences with the seasonal occurrence of the same taxa observed in a 6-year sediment-trap dataset from the western Sargasso Sea. Thus information on the ecologic preferences of individual taxa determined in one region cannot necessarily be applied directly to another area. In the northern Gulf of Mexico 90% of the total flux of Globorotalia truncatulinoides tests to sediments occurs in January and February. Mg/Ca and d 18 Ο measurements indicate that nonencrusted forms of Gt. truncatulinoides calcify in the upper-surface-mixed zone. Thus, analyses of nonencrusted Gt. truncatulinoides in sediments of the northern Gulf of Mexico have potential for monitoring past conditions in the winter-surface-mixed layer. The relatively low overall abundance of Globigerinoides ruber (white) in sediment-trap samples is anomalous because Gs. ruber (white) is one of the most abundant foraminifers in>150 µm census data from northern Gulf of Mexico Holocene sediment core samples. Globigerinoides ruber (pink) is a relatively persistent and common component of the sediment-trap samples. Thus Gs. ruber (pink) has potential as a proxy for mean annual sea-surface temperature in the Gulf of Mexico

Journal of Coastal Research↗

USGS2011

Globorotalia truncatulinoides (dextral) Mg/Ca as a proxy for Gulf of Mexico winter mixed-layer temperature: evidence from a sediment trap in the northern Gulf of Mexico

Three years of weekly- to biweekly-resolved sediment-trap data show that almost 90% of the total flux of tests of the planktic foraminifer Globorotalia truncatulinoides to sediments in the northern Gulf of Mexico occurs in January and February. Comparison of δ 18 O from tests of non-encrusted Gl. truncatulinoides in sediment-trap samples with calculated calcification depths indicates that the non-encrusted individuals secrete their test in the winter surface-mixed layer, most likely at the bottom of the surface mixed zone. Mg/Ca-temperature estimates from non-encrusted Gl. truncatulinoides in sediment-trap samples are consistent with observed temperatures at the calcification depths inferred from the δ 18 O data. In contrast, Mg/Ca-temperature estimates from encrusted Gl. truncatulinoides in sediment-trap samples indicate the crust is formed in cooler (deeper) waters. A preliminary study in a core recovered near the sediment-trap site demonstrates that non-encrusted and encrusted forms of Gl. truncatulinoides in sediment samples show a similar offset in Mg/Ca values as observed in sediment-trap samples. A short (~ 100 years) Mg/Ca record from non-encrusted Gl. truncatulinoides indicates a warming trend that coincides with a warming trend in mean-annual sea-surface temperature recorded by Mg/Ca in Globigerinoides ruber (white) from the same core. These findings suggest Mg/Ca from non-encrusted Gl. truncatulinoides has clear potential as a proxy for past winter mixed-layer temperature.

Marine Micropaleontology↗

USGS2011

Seasonal Flux and Assemblage Composition of Planktic Foraminifera from the Northern Gulf of Mexico, 2008-2009

The U.S. Geological Survey established a sediment trap in the northern Gulf of Mexico to collect time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the 2008 time-series data to include results from 2009. Ten species, or varieties, of planktic foraminifers constitute >90 percent of the assemblage: Globigerinoides ruber (pink and white varieties), Gs. sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group, Gt. truncatulinoides, Pulleniatina spp., Orbulina universa, and Neogloboquadrina dutertrei. The mean daily flux is about 215 tests per square meter per day, with maximum fluxes of >800 tests per square meter per day during early February and minimum fluxes of <20 tests per square meter per day during early October. Globorotalia truncatulinoides shows a clear preference for the winter and continues to provide the greatest number of tests for 2009, consistent with data from 2008. Globigerinoides ruber (white variety) flux increased more than 3 orders of magnitude from an average of 3 tests per square meter per day in 2008 to 11 tests per square meter per day in 2009. However, though Gs. ruber (white) abundance increased from 1.5 percent in 2008 to 4.9 percent in 2009, it continues to be a minor contributor to the total assemblage composition, in contrast to assemblage records from nearby sediments that indicate Gs. ruber (white) typically comprises approximately 20-30 percent of the assemblage.

Open-File Report↗

USGS2011

Seasonal flux and assemblage composition of planktic foraminifera from the northern Gulf of Mexico, 2008-2010

The U.S. Geological Survey anchored a sediment trap in the northern Gulf of Mexico to collect seasonal time-series data on the flux and assemblage composition of live planktic foraminifers. This report provides an update of the previous time-series data to include results from 2010. Ten species, or varieties, of planktic foraminifers constituted ~90 percent of the assemblage: Globigerinoides ruber (pink and white varieties), Gs. sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group, Gt. truncatulinoides, Pulleniatina spp., Orbulina universa, and Neogloboquadrina dutertrei. The mean daily flux was 219 tests per square meter per day (m -2 day -1 ), with maximum fluxes of >600 tests m -2 day -1 during late December and minimum fluxes of <40 tests m-2 day-1 during late August. Globorotalia truncatulinoides showed a clear preference for the winter, consistent with data from 2008 and 2009. Globigerinoides ruber (white variety) flux data for 2010 (average 29 tests m -2 day -1 ) showed a steady increase of about a factor of 3 since 2009 (average 11 tests m -2 day -1 ), and an almost 10-fold increase from the 2008 flux (average 3 tests m-2 day-1). The progressive increase in flux resulted in a relatively large increase in percent abundance of total assemblage from 2008 (1.5 percent) to 2010 (12.4 percent). In addition, though Gs. ruber (white) percent abundance increased from 4.9 percent in 2009 to over 12 percent in 2010, it continued to occur in lower abundance than the 20-30 percent indicated by dead-assemblage records from nearby sediments.

Open-File Report↗

USGS2010

Gulf of Mexico Climate-History Calibration Study

Reliable instrumental records of past climate are available for about the last 150 years only. To supplement the instrumental record, reconstructions of past climate are made from natural recorders such as trees, ice, corals, and microfossils preserved in sediments. These proxy records provide information on the rate and magnitude of past climate variability, factors that are critical to distinguishing between natural and human-induced climate change in the present. However, the value of proxy records is heavily dependent on calibration between the chemistry of the natural recorder and of the modern environmental conditions. The Gulf of Mexico Climate and Environmental History Project is currently undertaking a climate-history calibration study with material collected from an automated sediment trap. The primary focus of the calibration study is to provide a better calibration of low-latitude environmental conditions and shell chemistry of calcareous microfossils, such as planktic Foraminifera.

Fact Sheet↗

USGS2009

Seasonal Flux and Assemblage Composition of Planktic Foraminifera from the Northern Gulf of Mexico

A year-long sediment-trap experiment was conducted in the northern Gulf of Mexico (GOM) between January and December 2008 to study the flux and assemblage composition of planktic foraminifera from the region for comparison with concurrent hydrographic and climatic measurements. Ten species, or varieties, of planktic foraminifera constitute >80 percent of the assemblage: Globigerinoides ruber (pink and white varieties), Gs. sacculifer, Globigerina calida, Globigerinella aequilateralis, Globorotalia menardii group, Gt. crassaformis, Gt. truncatulinoides, Pulleniatina spp., and Neogloboquadrina dutertrei. The mean daily flux is about 200 tests per meter square per day (m-2 day-1) with the maximum fluxes of >600 tests m-2 day-1 occurring during October-March and minimum fluxes of <30 tests m-2 day-1 during April-June. The annual flux is weighted toward October-March; approximately 73.2 percent of the total annual flux is produced during this period, while the April-June and July-September fluxes make up 14 percent and 12 percent, respectively. During 2008, Gs. ruber (white) contributed ~1.5 percent to the total annual flux and averaged 4.5 percent during April-September, the period of highest fluxes for this species. Results from previous work in the GOM show Gs. ruber (white) contributing 20-30 percent of the late Holocene sediment record.

Open-File Report↗