My PhD research 2 paleoceanography

Hi everyone. I hope that you are absolutely great. For this post I am sharing some details about my first subjects. I shared the abstract in a last post but even that. But now I want to tell you a bit more about it.

Paleoceanography in canadian arctic

SCIENTIFIC BACKGROUND:

Sea ice plays an important role in the Arctic climate system by modulating the exchange of heat between a warm ocean and a cold atmosphere. During the past 30 years, satellite data indicate increasing temperatures and an accelerated reduction in the Arctic sea ice extent in summer, together with an overall decline of volume and thickness (IPCC, 2013). Likewise, climate scenarios derived from general circulation models predict important changes for the Arctic over the next 80 years in response to the actual warming trend (IPCC, 2013). However, examining trends over a short period (<30 years) is not sufficient to understand the impact of long-term climate change on sea ice extent. Thus, to place the reduction of Arctic sea ice in perspective, it is necessary to know the history of Arctic sea ice in the geologic past (Polyak etal., 2009). In the Arctic Ocean, bulk mineralogy and clay minerals as well as trace metal elements can be used to trace the pathways of sea ice, to decipher the source areas of sea ice and deep-sea sediments and to elucidate transport processes (Wahsner et al., 1999; Montero-Serrano et al., 2009).

Consequently, the mineralogy and elemental geochemical signatures of sedimentary sequences from the Arctic continental margins and surrounding coasts can provide clues on the natural sea ice variability through time. For this purpose, the international program CASES collected in 2004 several surface and sediment core samples covering the Holocene time (last 10,000 years) in the Mackenzie-Beaufort Sea Slope and Amundsen Gulf (Rochon and onboard participants, 2004). These sediment cores are characterized by high sedimentation rates (~110-120 cm/ka) and are particularly sensitive to changes in the past sea ice cover because it rests beneath the present ice margin of the permanent Arctic ice pack (Rochon and onboard participants, 2004).

Based on it we designed a PhD thesis drive to used geochemical and mineralogical tracer to explain the provenance sedimentary in this region. The tittle of my research is:

Evaluation of the sedimentary dynamics of the continental margin of the sea of Beaufort and Gulf of Amundsen (Arctic Ocean): paleoceanographic and paleoclimatic implications during the Holocene.

Thus, we developed three subjects to reach this purpose.
The first one oriented to know how the sedimentary dynamic in this basin is, using magnetic susceptibility and others magnetic parameters (hysteresis loops), and mineral/geochemical contents.

The second one consists in the reconstruction of the dynamic sedimentary around the last 4,500 years. In this case we used sedimentary cores (boxcore, trigger weight core and piston core) collected on Mackenzie slope.

Finally, the third one considers the clays as a possible tracer, so we analyzed Smectite, Kaolinite, illite and chlorite contents in surface and core sediments.

Here, my first article before I shared the abstract.

Mineralogical, geochemical, and magnetic signatures of surface sediments from the Canadian Beaufort Shelf and Amundsen Gulf (Canadian Arctic)

Introduction
Sedimentation in the Arctic Ocean is characterized by high terrigenous input from the surrounding continents with different petrographic signatures [Harrison et al., 2011]. These sediments are delivered into the Arctic Ocean mainly as suspended particulate matter and bed loads from several large river systems (notably, the Mackenzie, Kolyma, Lena, Ob, Yenisei, Pechora, and Severnaya Dvina) [Holmes et al., 2002; Wagner et al., 2011] and from coastal erosion, and then dispersed by ocean currents (summarized in Stein [2008]). Furthermore, in shallow margins, suspended terrigenous particles can also be incorporated in sea ice during its formation and then be transported via ocean currents over long distances throughout the Arctic Ocean, to finally settle far from their source of origin [e.g., Bischof et al., 1996; Darby et al., 2012, 2006]. Taking this into account, a number of studies have characterized the mineralogical and geochemical composition of the detrital sediments over the continental shelf from the Eurasian Basin [e.g., Vogt, 1997; Schoster et al., 2000; Viscosi-Shirley et al., 2003; Stein, 2008; Bazhenova, 2012], Chukchi Sea-Bering Strait [e.g., Asahara et al., 2012; Linsen et al., 2014], and Chukchi-Alaskan margin [e.g., Naidu et al., 1982; Naidu and Mowatt, 1983; Ortiz et al., 2009; Darby et al., 2012] to decipher: (1) variations in detrital particle provenance, (2) climate and atmospheric circulation changes in the source areas on adjacent landmasses, and (3) changes in sediment propagation and ocean-current pathways. However, few studies provide a general view of the surface detrital provenances and sediment-dispersal patterns within the Mackenzie-Beaufort Sea Slope and Amundsen Gulf [e.g., Naidu et al., 1971; Bornhold, 1975; Pelletier, 1975; Davidson et al., 1988; Hill et al., 1991; Darby et al., 2011; Vonk et al., 2015] compared to other Arctic continental shelf regions. To our knowledge, no general mineralogical and geochemical distributions of the Canadian Beaufort Shelf and Amundsen Gulf are available today. Such studies may provide a baseline to better interpret, in terms of sediment dynamics and climate change, the mineralogical and geochemical signatures preserved in the southern Beaufort Sea sedimentary records, which may then help to place current western Arctic climate change [e.g., Kwok et al., 2009] into its broader context. In this study, a multiproxy analysis was carried out on the bulk detrital fraction of surface sediment samples from the Mackenzie-Beaufort Sea Slope and Amundsen Gulf in order to: (1) characterize the spatial distribution patterns of siliciclastic grain size, magnetic properties, bulk minerals, and elemental geochemistry in surface sediments; (2) identify different sedimentary provinces, source areas, and transport pathways of terrigenous material; and (3) better constrain modern sediment dynamics within the western Canadian Arctic. Overall, this study provides a unique opportunity to compare mineralogical, geochemical, magnetic, and siliciclastic grain-size signatures within the Mackenzie-Beaufort Sea Slope and Amundsen Gulf area.

Like you can notice I needed to learn how use some lab equipment e.g. AGM (magnetometer, X-ray diffractometer and X-ray fluorescence spectrometer, and I was a kind of big challenge because the training was in English, the guides in French, and me I speak Spanish but even that I could learn.

Picture 1, show the equipment used for magnetic analyses and picture 2 a sequence for mineralogical analyses (both image were prepared for @geadriana and every picture inside too)

Some details about analytical procedure

Bulk Magnetic Properties
Low-field magnetic susceptibility (klf) was measured on bulk sediment samples using a Bartington MS2E. The klf values primarily reflect changes in the ferrimagnetic concentration (e.g., magnetite or titanomagnetite), but they are also sensitive to magnetic grain-size variations. In order to explore the possible presence of superparamagnetic particles,
magnetic susceptibility was measured in some bulk sediment samples, at low (0.465 kHz; klf) and high (4.65 kHz; khf) frequencies on a Bartington Susceptibility Meter (model MS2B) with a dual-frequency sensor. The sample measuring time was 10 s. Each measurement was repeated five times and the readings were averaged. The measurement of hysteresis loops and derived properties, including saturation remanence (Mr), saturation magnetization (Ms), bulk coercive force (Hc), and remanent coercive force (Hcr) were determined using an alternating gradient force magnetometer (AGM) MicroMag 2900 from Princeton Measurements Corporation. The Mrs/Ms and Hcr/Hc ratios can be used as grain-size proxies (the so-called Day plot) as well as to identify the magnetic domain state when the principal remanence-carrier mineral is magnetite [Day et al., 1977; Dunlop, 2002; Stoner and St-Onge, 2007].

Bulk Sediment Mineralogy and Elemental Geochemistry

Before the bulk mineralogical and geochemical analysis, the sediment samples were rinsed five times with distilled water after the removal of organic matter fraction with 10 mL of hydrogen peroxide (30% H2O2). Next, sediment samples were ground with a McCrone micronizing mill using 5 mL of ethanol and grinding times of 5–10 min to obtain a homogeneous powder. The slurry was oven-dried oven-dried at about 608C and then slightly homogenized with an agate mortar to prevent any agglomeration of finer particles during drying. Aliquots of these sediment samples were used for bulk mineralogical and geochemical analysis.

Bulk mineral associations were studied by X-ray diffraction (XRD). The random powder samples were sideloaded into the holders and analyzed on a PANalytical X’Pert Powder diffractometer. This method permits the semiquantification of whole-sediment mineralogy with a precision of 5–10% for phyllosilicates and 5% for nonphyllosilicate minerals.

A total of 14 elements (Al, Si, K, Mg, Ca, Ti, Mn, Fe, P, Sr, V, Cr, Zn, and Zr) were analyzed by energy dispersive X-ray fluorescence (EDXRF) spectrometry using a PANalytical Epsilon 3-XL. Before EDXRF analysis, loss on ignition (LOI) was determined gravimetrically by heating the dried samples up to 9508C for 2 h. Subsequently, samples were treated by borate fusion in an automated fusion furnace (CLAISSEVR M4 Fluxer). Samples weighing _0.6 g were mixed with _6 g of lithium borate flux (CLAISSE, pure, 49.75% Li2B4O7, 49.75% LiBO2, 0.5% LiBr). The mixtures were melted in Pt-Au crucibles (95% Pt, 5% Au), and after fusion, the melts were cast to flat disks (diameter: 32 mm; height: 3 mm) in Pt-Au moulds. Acquired XRF spectra were processed with the standardless Omnian software package (PANalytical). The resulting data are expressed as weight percent (wt.%; Al, Si, K, Mg, Ca, Ti, Mn, Fe, P) and micrograms per gram (lg/g; V, Cr,Zn, Sr, Zr). Procedural blanks always accounted for less than 1% of the lowest concentration measured in the sediment samples. Analytical accuracy and precision were found to be better than 1–5% for major elements and 5–10% for the other elements, as checked by an international standard (USGS SDC-1) and analysis of replicate samples.

I can say that with these equipment we can obtain important results, and they sequential and automatic analyses are useful in thus research field

Conclusions

Now some conclusion

The spatial variability of continental input, surface currents, and redox conditions within the Mackenzie- Beaufort Sea Slope and Amundsen Gulf was investigated through analyses of the grain size, magnetic properties, and the mineralogical and geochemical composition of 34 surface sediment samples. The results of this research yield the
following generalizations and conclusions:

The mineralogical, geochemical, and magnetic signatures of surface sediments allowed the identification of four provinces with distinct sedimentary compositions: (1) the Mackenzie Trough-Canadian Beaufort Shelf, characterized by minerals (phyllosilicates, Fe-oxides, magnetite) and elements (Al-K-Ti-Fe-Cr-V-Zn- P) derived mainly from the Mackenzie River discharges; (2) southwestern Banks Island, characterized by the association of dolomite-K-feldspar and Ca-Mg-LOI mainly supplied from coastal cliff erosion of Pleistocene potassium- and carbonate-rich glacial tills as well as clastic sedimentary rocks cropping out on the island; (3) the central Amundsen Gulf, which represents a transitional zone typified by intermediate phyllosilicates-magnetite-K-feldspar-dolomite and Al-K-Ti-Fe-Mn-V-Zn-Sr-Ca-Mg-LOI contents resulting from a detrital mix between the Mackenzie River discharges and coastal erosion of southwestern Banks Island; and (4) the mud volcanoes distinguished by the association quartz-plagioclase-authigenic carbonate and Si-Zr contents, as well as high magnetic susceptibility values resulting from the remobilization of glacial tills deposited in the subsurface of the Canadian Beaufort Shelf; and Our mineralogical data corroborate that K-feldspar/plagioclase and quartz/(K-feldspar1plagioclase) ratios [Vogt, 1997], together with detrital carbonate (dolomite), can be successfully used to track changes in terrigenous sediment input from the Canadian Beaufort Sea, Eurasian shelf, and Bering Strait.

Taken as a whole, our data provide a baseline for future studies using the mineralogical, geochemical, and magnetic signatures of sediment cores from the Mackenzie-Beaufort Sea Slope and Amundsen Gulf in order to reconstruct and document past variations in continental inputs and sediment dispersal related to climate changes.

Maybe the most important contribution in this research is that we could propose a model with mineralogical data and using of course statistical tools.