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Holocene oceanographic variation in the Godthåbsfjord region, SW Greenland, using diatom proxy

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Abstract

Godthåbsfjord region is composed of a sill fjord (190-km-long) and the adjacent continental shelf located in the SW Greenland. The fjord is composed of number of branches with surface area of 2013 km2 and is directly connected to the Greenland Ice Sheet. The shelf area is influenced by the oceanic current carrying Atlantic water masses. Study Material was collected from the shelf area (64⁰ 27.0694” N, 52⁰ 47.5783” W) from 495m water depth. sediment core SA13-ST3-16R retrieved using Rumohr Lot corer during R/V Sanna cruise in 2013. The core was sampled at 2 cm intervals and samples were subsequently processed using standard laboratory procedures and light microscopy. The aim of our study is to investigate the changes in diatom species composition in Godthåbsfjord region, SW Greenland over the past centuries based on high-resolution diatom record. We will present qualitative and quantitative reconstruction of oceanographic changes, i.e sea ice concentration and surface water temperature. The quantitative reconstruction will be done using recently developed diatom calibration dataset for the transfer function-based reconstructions of the West Greenland paleoenvironment Krawczyk et al. (2017).
Holocene oceanographic variation in the Godthåbsford region,
SW Greenland, using diatom proxy
Adrian Kryk1, Diana W. Krawczyk2, Marit-Solveig Seidenkrantz3 & Andrzej Witkowski1
1 Palaeoceanology Unit, Faculty of Geosciences, University of Szczecin, Szczecin, Poland
2 Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland
3Centre for Past Climate Studies, Department of Geosciences, Aarhus University, Århus, Denmark
INTRODUCTION
Greenland is the world's largest, non-continental island located between latitudes 59° and 83°N,
and longitudes 11° and 74°W. Greenland borders with Atlantic Ocean to the East, with the Arctic Ocean to the North
and Baffin Bay to the West. Three-quarters of Greenland is solely covered by the permanent ice sheet. Although
atmospheric temperatures in the Arctic have generally increased in the last century, the problem of temperature
changes in Greenland region is still strongly debatable. Firstly, Arctic temperatures are very variable, making
it difficult to identify long-term trends, particularly on a regional scale. Secondly, only until recently, the area of
the North Atlantic, including SW Greenland region, was one of the few areas in the world where cooling
was observed, however in the period 1979-2005 the trend reversed and strong warming was observed
(Lemke et al. 2007). The oceanographic variability in the West Greenland shelf region is governed by water masses
pushed by the West Greenland Current, seasonal sea ice cover and glacial ice from the Greenland Ice Sheet.
Our study aims to investigate the oceanographic changes in SW Greenland over the past four centuries (1600-2010)
based on high-resolution diatom record using both, qualitative and quantitative methods.
MATERIAL AND METHODS
Study material was collected from the Fyllas Banke (64 26.7 N, 52 47.6 W), i.e. shelf area located north-west
from Godthåbsfjord region, SW Greenland (Figure 1). Sediment core SA13-ST3-16R was retrieved from 495m
water depth using Rumohr Lot corer during R/V Sanna cruise in 2013. To obtain high-resolution diatom record
the 52-cm long core was sampled at 2 cm intervals and samples were subsequently processed using standard
laboratory procedures and light microscopy. Average sedimentation rate on the shelf area for the last 400 years
was estimated on level 0.7mm/yr. The chronology was based on combined Pb210 and AMS 14C dates from
a parallel gravity core and was conducted at Aarhus University. Statistical analyses (i.e. 'transfer function')
were modified from Krawczyk et al. (2017).
RESULTS
The analyzed core covers the time interval from 1600 AD to 2010 AD. We identified
128 diatom species representing 50 diatom genera. 23 (18%) taxa were identified
to the genus level and XX to a species level. The most abundant species were
Thallasiosira antarctica var. borealis (15%) and Thallasiosira kushirensis (15%).
Among dominant species (>1% of all taxa) were also: Fragilariopsis oceanica (7%),
Bacteriosira bathyomphala (6%), Grammatophora angulosa var. islandica (5%),
Fragilariopsis cylindrus (5%), Cocconeis costata (3%), Coscinodiscus radiatus (3%),
Chaetoceros diadema (2%), Chaetoceros furcellatus (2%), Fossula arctica (2%),
Fragilariopsis reginae-jahniae (2%), Grammatophora sp. (2%) , Porosira glacialis
(2%), Rhizosolenia borealis (2%), Thalassionema nitzschioides (3%),
Thalassiotrix sp. (2%), Thallasiosira hyalina (2%), Bacillaria paxillifera (1%),
Navicula distans (1%). Record of six dominant species (>5% of all taxa in all
samples) was compared to reconstructed oceanographic parameters (Figure 2),
i.e.: April Sea Ice Concentration (SIC), July Sea Surface Temperature (SST)
and - new for diatom-based reconstructions - September Sea Surface Salinity (SSS).
DISCUSSION
The most pronounced oceanographic changes off SW Greenland occurred during the last few decades as a result of interplay between sea ice variability and water salinity.
The average April SIC was low (c. 13%), however a strong peak of 56,5% was recorded at 1965. This peak was accompanied by a clear drop in salinity (33.2 PSU). To compare,
the average salinity between 1714 and 1920 was 34 PSU. This could be interpreted as freshening of surface waters induced by extensive sea ice cover or intense inflow of fresh
water masses from the Greenland Ice Sheet or from the Arctic Ocean. Interestingly, this salinity drop coincides with the ‘Great Salinity Anomaly’ identified in the mid-to-late 1960s
(Dickson et al. 1988 ). July SST during last 400 years varied only slightly from a minimum of 2,9 to a maximum of 4,7 C and total average of 4C. 4C is a typical surface water
temperature in SW Greenland during summer. Waters offshore SW Greenland were very productive, more than 4 mln valves per one gram of sediment at each sampled depth.
Average productivity was nearly 15 million valves/gram with maximum of 32 mln valves/gram at1758 and 1788 and 30 mln valves/gram at 1877.
ACKNOWLEDGEMENTS
The authors wish to thank the Grønlands Forskningsråd and
Greenland Institute of Natural Resources for funding the
project ClimaGreen. We acknowledge Danish Council for
Independent Research for funding the 2013 R/V Sanna cruise
to SW Greenland waters in the frame of ‘Past4Future’ project
and Aarhus University for funding geochronology and XRF
scanning. We thank the Greenland Ecosystem Monitoring
(GEM) Programme for providing access to present-day
phytoplankton reference database. The ‘transfer function’
calibration dataset was developed at Greenland Institute of
Natural Resources (contact: dikr@natur.gl).
REFERENCES
Dickson RR, Meincke J, Malmberg S-A, Lee AJ (1988) The “Great Salinity Anomaly” in the North Atlantic, 19681982. Prog Oceanogr 20:103151
Krawczyk, D. W., A. Witkowski, M. Moros, J. M. Lloyd, J. L. Høyer, A. Miettinen, and A. Kuijpers (2017), Quantitative reconstruction of Holocene sea ice and sea surface temperature
off West Greenland from the first regional diatom data set, Paleoceanography, 32, 1840, doi:10.1002/2016PA003003.
Lemke, P., J. Ren, R.B. Alley, I. Allison, J. Carrasco, G. Flato, Y. Fujii, G. Kaser, P. Mote, R.H. Thomas and T. Zhang (2007), Observations: Changes in Snow, Ice and Frozen Ground.
[In:] Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M. Tignor and H.L. Miller (eds.), Climate Change 2007: The Physical Science Basis. Contribution of Working
Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
Greenland
NUUK
Fyllas Banke
SA13-ST3-16R
Figure 1. Location of SA13-ST3-16R core
2000
1950
1900
1850
1800
1750
1700
1650
1600 10 10 10 10 10 10 20 40 4 34 10 30
20
20
April SIC
(%) July SST
(C) September
SSS (PSU) Productivity
(mln v/g)
Calendar years
Figure 2.
Fragilariopsis
cylindrus
Figure 4. SEM images of dominant species.
A-B: T. antarctica var. borealis internal view and external view of resting spore.
C-D: T. kushirensis resting spores (external and internal view).
E: B. bathyomphala (external view).
Figure 3. Percentage plot of the dominant diatom species (>5%) along with reconstructed
environmental variables
A B C D
E
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Article
Holocene oceanographic conditions in Disko Bay, West Greenland were reconstructed from high-resolution diatom records derived from two marine sediment cores. A modern dataset composed of 35 dated surface sediment samples collected along the entire West Greenland coast accompanied by remote sensing data were used to develop a diatom transfer function to reconstruct April Sea Ice Concentration (SIC) supported by July Sea Surface Temperature (SST) in the area. Our quantitative reconstruction shows that oceanographic changes recorded throughout the last c. 11000 years reflect seasonal interplay between spring (April SIC) and summer (July SST) conditions. Our records show clear correlation with climate patterns identified from ice core data from GISP2 and Agassiz-Renland for the early to mid Holocene. The early Holocene deglaciation of western Greenland Ice Sheet was characterised in Disko Bay by initial strong centennial-scale fluctuations in April SIC with amplitude of over 40%, followed by high April SIC and July SST. These conditions correspond to a general warming of the climate in the Northern Hemisphere. A decrease in April SIC and July SST was recorded during the Holocene Thermal Optimum reflecting more stable spring-summer conditions in Disko Bay. During the late Holocene, high April SIC characterised the Medieval Climate Anomaly, while high July SST prevailed during the Little Ice Age, supporting previously identified anti-phase relationship between surface waters in West Greenland and climate in NW Europe. This anti-phase pattern might reflect seasonal variations in regional oceanographic conditions and large-scale fluctuations within the North Atlantic Oscillation and Atlantic Meridional Overturning Circulation.
Article
The widespread freshening of the upper 500–800m layer of the northern North Atlantic, which this paper describes, represents one of the most persistent and extreme variations in global ocean climate yet observed in this century.Though a range of explanations have been advanced to explain this event, including in situ changes in the surface moisture flux, this paper describes the Great Salinity Anomaly as largely (though not entirely) an advective event, traceable around the Atlantic subpolar gyre for over 14 years from its origins north of Iceland in the mid-to-late 1960s until its return to the Greenland Sea in 1981–1982. The overall propagation speed around this subpolar gyre is estimated at about 3cm s−1. Of the total salt deficit associated with the anomaly as it passed south along the Labrador Coast in 1971–1973 (about 72 × 109 tonnes), a deficit equivalent to about two thirds of this figure (47 × 109 tonnes) ultimately passed through the Faroe-Shetland Channel to the Barents Sea, Arctic Ocean and Greenland Sea during the mid-1970s.Possible effects on deep water formation and on the representativeness of historical section data are discussed.
  • R R Dickson
  • J Meincke
  • S-A Malmberg
  • A J Lee
Dickson RR, Meincke J, Malmberg S-A, Lee AJ (1988) The "Great Salinity Anomaly" in the North Atlantic, 1968-1982. Prog Oceanogr 20:103-151