Zviely dov

LEON RECANATI INSTITUTE FOR MARITIME STUDIES (RIMS), UNIVERSITY OF HAIFA, HAIFA 31905, ISRAEL.

Biodata of Michal Lichter, Dov Zviely, Micha Klein, and Dorit Sivan, authors of "Sea-Level Changes in the Mediterranean: Past, Present and Future - A Review"

Dr. Michal Lichter is currently a Postdoctoral Researcher in the Coasts at Risk and Sea-Level Rise (CRSLR) Research Group of the Future Ocean Excellence Cluster, based at the Institute of Geography, Christian Albrechts University, Kiel, Germany. She obtained her Ph.D. in Geography and Environmental Studies from the University of Haifa, Israel, in 2009. Dr. Michal Lichter's primary research interests are Coastal geomorphology, Geomorphological mapping, spatial analysis and GIS, shoreline changes, landform processes and environmental change, climate change, and sea-level rise.

E-mail: [email protected]

Dr. Dov Zviely is Researcher in the Leon Recanati Institute for Maritime Studies (RIMS), in the University of Haifa, Israel. His scientific areas are: (1) Coastal geomorphology and sedimentology; (2) continental shelf morphodynam-ics; (3) Quaternary coastal paleo-geography and geo-archeology; (4) Charts, maps, hydrography, and maritime history of the eastern Mediterranean Sea.

E-mail: [email protected]

A. Israel et al. (eds.), Seaweeds and their Role in Globally Changing Environments,

Cellular Origin, Life in Extreme Habitats and Astrobiology 15, 3-17

DOI 10.1007/978-90-481-8569-6_1, © Springer Science+Business Media B.V. 2010

Professor Micha Klein is currently Professor Assistant in the Department of Geography and Environmental Studies, in the University of Haifa, Israel. He obtained his Ph.D. in geomorphology at the school of geography, University of Leeds, UK. His scientific areas are: (a) Geomorphology with special interest in drainage basin dynamics and in coastal geomorphology and (b) Geomorphology of Israel.

E-mail: [email protected]

Dr. Dorit Sivan, Ph.D. in Geology, The Hebrew University of Jerusalem, the Faculty of Science, Institute of Earth Sciences, Department of Geology. At present, she is a Senior Lecturer and Head of the Department of Maritime Civilizations, University of Haifa, and a researcher in the Leon Recanati Institute for Maritime Studies (RIMS).

Her research interests are mainly:

(a) Reconstruction of the coastal environment, mainly during the Holocene, and its connection to human settlement.

(b) Indications for past sea levels over the last 20,000, and mainly the last 10,000 years, during which there was intensive occupation along the Israeli coast. These two subjects, the paleogeography and sea-level curves, are essential for the understanding of mankind's historical processes, and complement historical and archeological research. This field of research is interdisciplinary and linked to the application of diverse research methods.

E-mail: [email protected]

Micha Klein

Dorit Sivan

Micha Klein

Dorit Sivan

SEA-LEVEL CHANGES IN THE MEDITERRANEAN: PAST, PRESENT, AND FUTURE - A REVIEW

MICHAL LICHTER1, DOV ZVIELY2, MICHA KLEIN3, AND DORIT SIVAN4

'Coasts at Risk and Sea-Level Rise, Research Group, The Future

Ocean Excellence Cluster, Institute of Geography, Christian Albrechts

University, Kiel, 24098 Germany

2Leon Recanati Institute for Maritime Studies (RIMS),

University of Haifa, Haifa, 31905, Israel

3Department of Geography and Environmental Studies,

University of Haifa, Haifa, 3'905, Israel

4Department of Maritime Civilizations, University of Haifa,

Haifa, 3'905, Israel

1. Introduction

The study of geological and historical sea-level changes constitutes an important aspect of climate change and global warming research. In addition to the imminent hazards resulting from the inundation of low-lying areas along coastal regions, the rise in sea level can also cause erosion of beaches, salt intrusion into freshwater aquifers, and other damage to the coastal environment. The utmost importance of current changes in sea level is attributed to its impact on diverse ecological systems in coastal regions (Klein et al., 2004).

On time-scales of millions of years, geological processes, such as changes in ocean basin geometry caused by plate tectonics, are dominant in affecting sea-level change, whereas on shorter time-scales of years and decades, oceanographic and climatic factors are more dominant (Lambeck and Purcell, 2005).

On time-scales of centuries and millennia, sea-level change is affected mainly by eustatic (all types of water volume variations), glacio-hydro-isostatic, and tectonic factors. Eustatic changes are global and are defined as ice volume equivalent. Isostatic sea-level changes are regional, and result from changes of ice mass balance over the crust and water and sediment over the continental shelf and ocean floor. Vertical tectonic movements are local and are caused by geological uplift or subsidence. Glacio-hydro-isostatic change has a predictable pattern, whereas tectonics is less predictable (Lambeck et al., 2004). The best way for differentiating the global, regional, and tectonic processes in long-term records is by comparing observations and glacio-hydro-isostatic models that predict the combined global and regional components (e.g., Lambeck and Purcell, 2005, and references therein). Discrepancies between the observed and the model-predicted changes are attributed to local movements, whether induced by tectonic movements, sediment compaction, or other reasons.

For short-term records of decadal scale, distinguishing between the "eustatic" component and regional-local crustal movements can be conducted only with present-day measurements. This involves simultaneous measurements of relative sea-level changes by tide-gauge and land vertical movement by GPS or other geodetic techniques. Daily and seasonal changes are caused mainly by astronomical tides and other atmospheric and oceanic forcing mechanisms.

"Eustatic" sea-level changes do not actually exist because sea-level changes are spatially heterogeneous, at least over decadal time scales (Mitrovica et al., 2001). Isostatic and local factors affecting land levels may cause relative sea-level changes that vary from place to place throughout the world (Pirazzoli, 1996).

Over the past century, sea level rose by 1-2 mm/year, with nonlinear changes ("accelerations") in different places (Woodworth and Player, 2003; Church and White, 2006; Jevrejeva et al., 2006; Woodworth, 2008), inundating flat coastal areas, and disrupting natural freshwater environments as well as human habitat in many coastal and inland communities.

2. Mediterranean Sea-Level Change Since the Middle Pleistocene

"Global" sea-level curves indicate that during the last 600,000 years (ka), the sea reached a maximum elevation of 5-10 m above present sea level (asl) (Fig. 1) at least three times and dropped to more than 100 m below present sea level (bsl) at least five times (Waelbroeck et al., 2002; Schellmann and Radtke, 2004; Rabineau et al., 2006;

Sea Level Curve Rohling 2009
Figure 1. Global sea-level changes in the last 600 ka. (Modified after Waelbroeck et al., 2002; Rabineau et al., 2006; and Siddall et al., 2006.)

Siddall et al., 2006). The cyclic transition between glacial and interglacial cycles was about 100 ka (Shackleton, 2000), and the mean time between one glacial trough and the succeeding interglacial peak was about 20 ka.

Sea level during Marine isotope stage (MIS) 7.1, dated to between 202 and 190 ka, remained 18-9 m bsl (Bard et al., 2002), based on precise Uranium-Thorium (U-Th) dating of stalagmites from a currently submerged cave in Italy.

Sea level rose above its present level only at the peak of the last interglacial, some 125 ka ago (MIS 5e). In the Mediterranean, dating of the MIS 5e terraces is not certain, and at present there are indications of different levels, as summarized in Mauz and Antonioli (2009) and Stewart and Morhange (2009). The present elevations of the different sea-level indicators range between +175 and -125 m only in Italy because of tectonic reasons (Ferranti et al., 2006), or because of hydro-glacial adjustment of the crust (Antonioli et al., 2006). Studies in regions of the Mediterranean that are relatively tectonically stable, such as the coast of Israel (Sivan et al., 1999; Galili et al., 2007), western Sicily, and southern Sardinia, indicate that the Last Interglacial sea reached approximately 6 ± 3 m asl (Lambeck et al., 2004; Ferranti et al., 2006).

"Global" sea level later dropped to about 120 ± 5 m bsl, reaching its lowest levels during the Last Glacial Maximum (LGM), about 18 ka ago. In the Mediterranean, the longest record is found in Cosquer Cave, southern France, where Paleolithic wall paintings of horses dated to about 22 ka ago have been partially eroded by the recent rising sea water level (Lambeck and Bard, 2000 and references therein; Morhange et al., 2001).

Numerical models (Lambeck and Bard, 2000; Lambeck and Purcell, 2005) predicting sea-level changes during the last 18 ka allow estimation of the vertical movements by comparing the observations to the predictions summarized for all the Mediterranean by Stewart and Morhange (2009).

Since then, "global" sea level has been rising as a result of deglaciation and global warming (Fairbanks, 1989; Bard et al., 1990, 1996; Pirazzolli, 1991; Fleming et al., 1998; Rohling et al., 1998; Lambeck and Bard, 2000; Lambeck et al., 2002, 2004). At around 12.5 ka ago, "global" sea level rose rapidly to 70 m bsl. It continued to rise and reached 40 m bsl at the beginning of the Holocene. Levels lower than 20 bsl at the beginning of the Holocene have been observed in Israel, based on the submerged Pre-Pottery Neolithic site of Atlit Yam, situated at present 10-12 m bsl, with the bottom of one of the water wells at present 15.5 m bsl (Galili et al., 1988, 2005). Sea level continued to rise rapidly until the Mid-Holocene, when the rate slowed considerably (Lambeck and Bard, 2000; Bard et al., 1996; Lambeck et al., 2004; Poulos et al., 2009). Based on biological, sedimentological, and archeological indicators, sea-level studies around the Mediterranean indicate ±1 m bsl about 4 ka ago (Morhange et al. (2001) in the west Mediterranean, Lambeck et al. (2004) in Italy, Marriner et al. (2005) in Lebanon, and Sneh and Klein (1984), Galili et al. (1988, 2005), Nir (1997), Sivan et al. (2001, 2004), Galili and Sharvit (1998, 2000), and Porat et al. (2008) all from Israel, east Mediterranean). From about 4,000 until 2,000 years ago, there is ample archeological and biological (mainly biostructural) evidence available for sea-level reconstructions from all around the Mediterranean with better vertical accuracy of up to ±10 cm. During the Early Roman period, 2,000 years ago, sea level in the Mediterranean was 10-15 cm bsl. In Israel, Sivan et al. (2004) examined 64 coastal water wells in ancient Caesarea, and concluded that sea level was close to the present level during the Roman period. This conclusion agrees with the results found in Italy (Anzidei et al., 2008). For the Crusader period (eleventh to thirteenth centuries AD), lower levels of about 30 ± 15 cm bsl were estimated, based on the coastal water wells of Caesarea (Sivan et al., 2004; Sivan et al., 2008). These low levels are confirmed (with even lower estimated levels) by ongoing data from a few sites along the coast of Israel, based mainly on archeo-logical evidence (Sivan et al., 2008).

3. "Global" Sea-Level Observations During the Twentieth Century

There is a consensus among sea-level researchers that the "global" sea-level rise in the past 100 years has been considerably faster than in the previous two millennia (Douglas, 2001).

"Global" sea-level rise during the twentieth century (Table 1) is estimated by most researchers to be 1-2 mm/year (Peltier, 2001; Miller and Douglas, 2004; Church and White, 2006). Church and White (2006) calculated a significant acceleration of sea-level rise of 0.013 ± 0.006 mm/year during the twentieth century.

The employment of tide-gauging facilities began in the second half of the nineteenth century, markedly improving the accuracy of sea-level measurement. Tide-gauge stations were rare prior to 1870, while spatially widespread tide-gauge records are available only for the twentieth century. Tide-gauge measurements are considered the most accurate sea-level records available for the twentieth century (Miller and Douglas, 2004), but they suffer from problems of spatial and temporal discontinuity that make calculating "global" mean trends a difficult task. Since the 1990s, sea-level measurements have also been obtained by satellite altimetry, which are often used as complementary data for tide-gauge data (Cabanes et al., 2001; Church et al., 2004). At present, more information about sea-level change

Table 1. Estimates of the "global" mean sea-level contributions from 1961 to 2003 and 1993 to 2003, compared with the observed rate of rise. (Modified after Bindoff et al., 2007.)

Source

1961 to 2003

1993 to 2003

Thermal expansion

0.42 ± 0.12

1.60 ± 0.50

Glaciers and ice caps

0.50 ± 0.18

0.77 ± 0.22

Greenland ice sheet

0.05 ± 0.12

0.21 ± 0.07

Antarctic ice sheet

0.14 ± 0.41

0.21 ± 0.35

Sum

1.10 ± 0.50

2.80 ± 0.70

Observed

1.80 ± 0.50

3.10 ± 0.70

Difference (observed-sum)

0.70 ± 0.70

0.30 ± 1.00

is available than ever before: historical data sets from tide-gauges; new understanding of postglacial rebound; precise geodetic techniques for the estimation of vertical crustal motion, and finally, more a decade of satellite altimetry, providing more precise records of recent changes in mean sea level (Cazenave and Nerem, 2004). New altimeter measurements from the TOPEX/Poseidon and Jason-1 satellites since the beginning of the 1990s have revealed a much faster rise in sea level during 1993-2003 than the average twentieth century rate. Cazenave and Nerem (2004) calculated a 2.8 ± 0.4 mm/year rise for this period (3.1 mm/year if the effects of postglacial rebound are removed).

As mentioned earlier, sea-level changes are not uniform around the Globe, e.g., Church et al. (2004) recognized a maximum sea-level rise in the eastern Pacific off-equatorial area, and minima along the equator, in the western Pacific, and in the eastern Indian Ocean.

Table 1 summarizes the contributions of thermal expansion, glaciers and ice caps, and the two ice sheets to "global" sea-level rise since 1961, according to the Fourth Assessment Report (AR4) of the Intergovernmental Panel on Climate Change (IPCC). It is, however, noted in the report that the total "global" sea-level change budget has not yet been satisfactorily closed.

From 1961 to 2003, thermal expansion accounted for only 23 ± 9% of the observed rate of sea-level rise (Bindoff et al., 2007). Since 1993, the contribution of thermal expansion of the oceans to the total rise of sea levels has been about 57%. The contribution of glaciers and ice caps decreased to about 28%, and losses from the polar ice sheets contributed the remainder (IPCC, 2007).

4. Mediterranean Sea Levels During the Twentieth Century

Tsimplis et al. (2008) examined sea-level trends and interannual variability in the Mediterranean (Genova and Trieste) during the years 1960-2000. Although the observed values did not show a rise in sea level, when removing the atmospheric and the steric contributions, the residual trends revealed a significant rise of 0.7-1.8 mm/year. This rise was not uniform, as two different trends were distinguished. Between 1960 and 1975, there was no significant change in sea level, but from 1975 to 2000, sea level rose at a rate of 1.1-1.8 mm/year. They attributed part of the residual trend to local land movements (0.3 mm/year), and its major part to a global signal, probably mass addition, after 1975.

Klein and Lichter (2009) compared observed Mediterranean rates with the "global" rate, and found the sea-level rise in the Mediterranean over the twentieth century to be in agreement with the mean "global" sea-level rise during the twentieth century (1.1-2.4 mm/year). They also found that this trend has not been consistent throughout the century (Table 2; Fig. 2). Three distinctly different sea-level trends were recognized. The first lasted from the end of the nineteenth century to 1960, when relative sea level in the Mediterranean rose by rates slightly higher than the overall "global" trend (1.3-2.8 mm/year). In the second, from 1961 to 1989,

Table 2. Twentieth century sea-level trends in the Mediterranean. Linear trends from the four tide-gauging stations with the longest record in the Mediterranean. The trends are presented for the full record and for the three different trends during the twentieth century: until 1960, from 1961 to 1989, and from 1990 to 2000 (not enough data).

Sea-level Sea-level Sea-level

Sea-level change change change change

PSMSL PSMSL station Start of until 1960 1961-1989 1990-2000 full record station No. name record (mm/year) (mm/year) (mm/year) (mm/year)

230051 Marseille (FR) 1885 1.72

250011 Genova (FR) 1884 1.28

270054 Venice (Ponte 1909 2.77

della Salute) (IT)

270061 Trieste (IT) 1905 1.35

0.37

9.11

1.14

Figure 2. Linear sea-level trends from the beginning of the measurement until 1960, from 1961 to 1989, and from 1990 to 2000 in Marseilles (230051), Genoa (250011), Venice (270054), and Trieste (270061).

the observed measurements did not indicate significant changes in Mediterranean sea level. Since the beginning of the 1990s, a third, short-term trend of extremely rapid sea-level rise has been measured (4-17 mm/year). Table 2 presents sea-level trends of four Revised Local Reference (RLR) tide-gauging records in the Mediterranean, with a record of close to 100 years, available in the Permanent Service for Mean Sea Level (PSMSL) database. The stations are Marseille, Genova, Venice (with higher rates of relative sea-level rise due to subsidence in the first half of the century) and Trieste. Sea-level trends are shown for the period from the beginning of the measurement to 1960, from 1961 to 1989, from 1990 to 2000 (only Venice and Trieste had sufficient data), and for the entire record.

Klein and Lichter (2009) also found that the stability in sea level during 1961 and 1989 was the result of a rise in surface atmospheric pressure from 1961 to 1989, and that eustatic sea level has in fact been rising, but had been depressed by the rising air pressure. From 1990 onward, most gauging stations have showed an extremely high sea-level rise, 5-10 times the average twentieth century rise, and notably higher than the "global" average measured by TOPEX/Poseidon for the same years. This is in agreement with sea-level rates found in the eastern Mediterranean by Rosen (2002), who calculated a sea-level rise of 10 mm/year at the Hadera gauging station between 1992 and 2002, and Shirman (2004) who showed a 10 cm rise in sea level from 1990 to 2001 at the Ashdod and Tel Aviv tide-gauges.

New tide-gauge measurements (for location, see Fig. 3), presented in Table 3, show a slight decrease in the rate of Mediterranean sea-level rise in the first few years of the twenty-first century. The rates of sea-level rise were calculated from 27 Mediterranean PSMSL RLR tide-gauge records between 1990 and 2000, and between 1990 and 2006 (the full data sets currently available on the PSMSL website). In most stations, there has been a decrease in the rate of sea-level rise between 1990 and 2006 when compared with the trend between 1990 and 2000, but the rates remain considerably higher than the "global" and Mediterranean twentieth century rates. It is important to note that the periods considered here are short, and the

Figure

3. Location map of the tide-gauging stations presented in Table 3.

Figure

3. Location map of the tide-gauging stations presented in Table 3.

Table 3. Mediterranean sea-level trends from 1990s and onward. Linear trends are presented for 1990-2000, and where data were available trends extending to the mid-2000s were calculated.

Sea-level change

Sea-level change

during period

during period

PSMSL

PSMSL

1990-2000

No. of

1990-2006

No. of

station No.

station name

(mm/year)

years

(mm/year)

years

1

220011

Algeciras (ES)

3.32

10

2

220031

Malaga (ES)

8.62

10

3

220041

Almeria (ES)

9.58

8

4

220081

L'Estartit (ES)

4.50

11

5

270054

Venezia - Ponte della Salute (IT)

10.11

11

6

270061

Trieste (IT)

9.11

11

4.99

17

7

279003

Luka Koper (SL)

-1.20

9

8

280006

Rovinj (HR)

10.05

11

6.24

15

9

280011

Bakar (HR)

13.52

11

8.98

15

10

280021

Split Rt Marjana (HR)

9.90

11

7.33

15

11

280031

Split Harbor (HR)

9.45

11

7.96

15

12

280046

Sucuraj (HR)

11.02

10

7.40

14

13

280081

Dubrovnik (HR)

9.51

9

7.35

13

14

290001

Preveza (GR)

11.32

11

4.92

14

15

290004

Levkas (GR)

4.21

8

2.96

12

16

290014

Patrai (GR)

14.92

8

12.88

14

17

290017

Katakolon (GR)

17.26

8

6.21

12

18

290030

North Salaminos (GR)

4.88

8

19

290031

Piraeus (GR)

-16.15

8

20

290033

Khalkis South (GR)

7.54

8

21

290034

Khalkis North (GR)

1.68

10

5.71

15

22

290051

Thessaloniki (GR)

9.04

9

23

290061

Kavalla (GR)

-0.06

9

1.70

13

24

290065

Alexandroupolis (GR)

6.46

10

5.31

15

25

290071

Khios (GR)

17.98

9

5.17

12

26

290091

Leros (GR)

-0.08

8

-1.84

11

27

290097

Soudhas (GR)

7.36

10

trend they indicate might be merely an expression of a rising phase of an oscillating pattern. However, during no other short period in the twentieth century have tide-gauge records in the Mediterranean shown such an extreme trend.

5. Future Sea-Level Predictions

The AR4 of the IPCC (2007) predicted "global" sea-level rise of 0.18-0.59 m in 2090 and 2099, relative to 1990 and 1999 (about 2-6 mm/year) using several different future scenarios. These predictions, however, do not include uncertainties resulting from climate-carbon cycle feedbacks, or the full effects of changes in ice sheet flow. These factors are currently unknown, and therefore the upper values of these predictions are not considered upper bounds for sea-level rise.

The predictions take into consideration a contribution to sea-level rise due to increased ice flow from Greenland and Antarctica at the rates observed from 1993 to 2003. A linear increase in ice flow from the ice sheets with global average temperature change would increase the upper range of sea-level rise for these future scenarios by only 0.1-0.2 m (IPCC, 2007).

The IPCC AR4 predicts thermal expansion that contributes more than half of the average sea-level rise estimated for the twenty-first century, and land ice that loses mass increasingly rapidly. An important uncertainty relates to the question of whether discharge of ice from ice sheets will continue to increase as a consequence of accelerated ice flow, as has been observed in recent years. This would add to the sea-level rise, but quantitative predictions cannot be made with a high degree of confidence, owing to the limited understanding of the relevant processes (Bindoff et al., 2007).

The ranges of sea-level rise predictions of the AR4 are lower than those projected in the Third Assessment Report (TAR) of the IPCC (2001), because of improved information about some of the uncertainties of some contributions.

Recent attempts to predict future "global" sea-level rise confirm the ranges predicted by the IPCC reports, while others predict higher rates. Church and White (2006) estimate that if the twentieth century acceleration in sea-level rise (0.013 ± 0.006 mm/year) remains constant during the twenty-first century, sea-level would rise by 0.28-0.34 m from 1990 to 2100, a rise consistent with the middle range of the TAR and AR4 predictions.

However, Rahmstorf et al. (2007) compared sea-level predictions of the TAR with sea-level observations from the 1990s and 2000s, and found that the observations followed the upper limit of the predictions, including land-ice uncertainties. They calculated the rate of rise in the past 20 years to be 25% faster than in any other 20-year period in the last 115 years. Although they are aware of the short time interval, they conclude that these predictions may have underestimated sea-level change. Rahmstorf (2007) applied a semi-empirical methodology to project future sea-level rise by using the relations between "global" sea-level rise and global mean surface temperature. He suggests that the rate of sea-level rise is roughly proportional to the magnitude of warming above the temperatures of the pre-industrial age. This relation produced a constant of 3.4 mm/year/°C. Applying this to future IPCC scenarios, a sea-level rise of 0.5-1.4 m above the 1990 level is projected for 2100. Hence, he concludes that if the linear relations between sea-level rise and temperature that existed in the twentieth century persist through the twenty-first century, a rise of over 1 m for strong warming scenarios is not unlikely.

6. Summary

The past 600,000 years are characterized by glacial and interglacial cycles. During the glacial maxima, sea level dropped more than 100 m below its present level. Sea level in interglacial periods exceeded the present sea level by a few meters three times during that time.

During the LGM, about 18 ka ago, "global" sea level dropped by about 120 m below its present level. Since then, the transition of the global climate into an interglacial period was followed by a rapid sea-level rise until around 6,000 years ago, when there was a decrease in the rate of sea-level rise, and a relative stabilization at about the present level about 4,000 years ago.

In the Mediterranean, there are radiometric ages derived from different sea-level indicators that go back to the MIS 7.1, dated to between 202 and 190 ka ago. The last time that sea level rose above its present level was some 125 ka ago during the MIS 5e. There are ample well-dated indications for sea level during MIS 5e, located at present at different elevations due to vertical movements. There are biological, sedimentological, and mainly archeological data from the LGM, about 18 ka ago from all around the Mediterranean; the oldest being from Cosquer Cave, southern France, dated to about 22 ka ago. Sea level stabilized at almost the present level around 4,000 years ago with vertical accuracy of ±1 m. Later, 2,000 years ago, the rate of accuracy from different indicators (both biological and archeological) reaches ±10-15 cm, and fluctuations of tens of cm are recorded.

"Global" twentieth century sea-level rise is agreed by researchers to be considerably faster than in the previous two millennia. Most researchers estimate a "global" twentieth century rate of 1.0-2.5 mm/year. During the 1990s, the mean rate of "global" sea-level rise was significantly higher than the twentieth century mean rate (1.3-2.8 mm/year). Mediterranean twentieth century sea-level rise was close to the "global" rise, with the exception of the 1990s, when sea level in the Mediterranean rose at rates higher even than the unusually high "global" ones (up to three and four times the "global" 1990s rate). The rate of sea-level rise since the beginning of the 1990s has decreased in the first half of the current decade; however, it is still considerably higher than the twentieth century mean rate.

Future predictions of sea-level rise over the twenty-first century range from moderate amounts of less than 20 cm to much higher values of over 1 m. The uncertainties are attributed to the future contribution of Greenland and the Antarctic ice sheets, and uncertainties resulting from climate-carbon cycle feedback, as well as from other unpredicted proxies.

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Biodata of Dr. Linda Olsvig-Whittaker, author of "Global Climate Change and Marine Conservation"

Dr. Linda Olsvig-Whittaker is an Informatics Specialist in the Israel Nature and Parks Authority (INPA), headquartered in Jerusalem, Israel. She received her Ph.D. in Ecology and Evolutionary Biology at Cornell University (Ithaca, USA) in 1980. She was a Lady Davis Postdoctorate Fellow at the Technion (Haifa, Israel) during 1981-1982, followed by an year as a research scientist on the Brookfield Ecosystem Project (Flinders University, Australia). During 1984-1994, she was a research scientist for plant community ecology in the Mitrani Center for Desert Ecology (Ben Gurion University, Israel). She joined the Nature Reserves Authority in 1994 as Coordinator of Scientific Data, remaining in this position when the NRA became the Nature and Parks Authority. She is responsible for the management of the observational data in the INPA and currently heads the Israeli partnership in the EBONE project (European Biodiversity Observation Network, www.ebone.wur. nl). Dr. Olsvig-Whittaker is active in the Society for Conservation Biology, having served 5 years as communications officer for the Asia Section of SCB. She is also an editor for the journal Plant Ecology.

E-mail: [email protected]

A. Israel et al. (eds.), Seaweeds and their Role in Globally Changing Environments,

Cellular Origin, Life in Extreme Habitats and Astrobiology 15, 19-28

DOI 10.1007/978-90-481-8569-6_2, © Springer Science+Business Media B.V. 2010

GLOBAL CLIMATE CHANGE AND MARINE CONSERVATION

LINDA OLSVIG-WHITTAKER

Science and Conservation Division, Israel Nature and National Parks Protection Authority, 3 Am Ve Olamo Street, Givat Shaul, Jerusalem 95463, Israel

1. Introduction

Global climate change is real. Compilations of instrumental global land and sea temperatures back to the mid-ninteenth century provide strong evidence of a warming world and recent unusual warmth, with 9 of the 10 warmest years since 1850 occurring between 1997 and 2006. The most recent projections of global climate change due to the enhanced greenhouse effect suggest that global average temperature could warm by 1.1°C to 6.4°C over 1980-1999 values by 2100, with best estimates ranging from 1.8°C to 4.0°C. These estimates are generally consistent (although not strictly comparable) with the earlier projections of 1.4°C to 5.8°C, and are based on more climate models of greater complexity and realism and better understanding of the climate system (Lough, 2007).

Global climate has always fluctuated, but the scale tends to be over tens of thousands of years. In the last few centuries, we have experienced an accelerated rate of climate change, largely due to the release of industrial gases, and especially of carbon dioxide (CO2). By 2100, atmospheric CO2 is expected to exceed 500 ppm, and global temperatures to rise at least 2°C, exceeding conditions of the past 420,000 years (Hoegh-Guldberg et al., 2007). The Earth's radiative heat balance is currently out of equilibrium, and mean global temperatures will continue to rise for several centuries even if greenhouse gas emissions are stabilized at present levels (IPCC, 2001).

In the marine environment, ongoing studies by NOAA (United States National Oceanic and Atmospheric Administration) scientists show that changes in surface temperature, rainfall, and sea level will be largely irreversible for more than 1,000 years after carbon dioxide emissions are completely stopped (Solomon et al., 2009). Global sea levels are predicted to rise for the next 1,000 years; the minimal irreversible global average sea level rise is predicted to be at least 0.4-1 m in the year 3000, and possibly double that if CO2 peaks at 600 ppm. (Present concentrations are around 385 ppm.) The rise in sea level will be mainly due to two factors: thermal expansion of the ocean's water and input from melting ice.

Possibly as important as sea-level rise there will be changes in ocean chemistry (Diaz-Pulido et al., 2007). Continued emission of CO2 will acidify sea waters. Oceanic pH is projected to decrease by about 0.4-0.5 units by 2100 (e.g. a change from pH 8.2 to 7.8).

The Mediterranean Sea, a somewhat special case as a smaller enclosed basin, will have additional problems of higher surface water temperatures and rising salinity. Sevault et al. (2004), using the high-resolution Ocean Regional Circulation Model OPAMED8, anticipated a surface temperature rise of 2.5°C by 2100, and a regionally variable salinity increase between 0.12 and 0.19 psu, with about 0.4 psu increase in the Aegean and Adriatic seas, in a scenario for years 2060 to 2100.

Israel fits the general pattern of rising sea levels. Monthly averaged sea-level changes at the Mediterranean coast of Israel during 1992-2008 show a rise of 8.5 cm in 16 years. (Data from the Hadera GLOSS station 80, operated by Israel Oceanographic and Limnological Research Institute.)

2. Responses to Global Climate Change

The impact of global climatic change on marine systems seems to be mainly felt in two areas. First is the impact on coastal waters, where rising sea-level shifts the distribution of species, and surface waters become warmer. Second, and more dramatic, is the impact on coral reefs.

2.1. COASTAL ZONES

Sixty percent of all human beings live on a 60-km wide strip of coastal zone in the world. Marine coastal water is the seat of 14-30% of the ocean's primary production, and 90% of the fishing catch. Sea-level rise will shift the habitats especially of coastal waters (UNEP-MAP-RAC/SPA, 2008).

Some local studies have been carried out on the effects of climate change in marine communities (Parmesan, 2006). In Monterey Bay, Sagarin et al. (1999) observed a decline in northern species and an increase in southern species. Similar patterns were seen in the English Channel (Southward et al., 1995, 2005) with a decline in cold-adapted fish and increase in warm-adapted fish. Similar patterns were observed in invertebrates (Parmesan, 2006).

Harley et al. (2006) predict changes in pH of oceans without precedent in the last 200-300 million years. Upwelling could either increase or decrease. Landward migration of intertidal habitats and biota may be impeded by anthropogenic infrastructure (sea walls, etc.). An increase in storm damage is expected. Biological interactions are likely to be affected (for example, sea star Pisaster ochraceus is quite likely to be more active in a warmer climate, with larger effects on mussel beds). Harley et al. (2006) expect "squeeze effects," with potential shifts in distribution limited by a physical barrier (sea bottom, etc.) leading to local extinctions.

There is difficulty in predicting the effects of global climate change on diversity of marine plant life. However, the competitive interaction of sea grasses and macroalgae may be predicted, with CO2 levels rising, and intertidal macroalgae already at CO2 saturation (Beardall et al., 1998). Review of literature so far (Short and Neckles, 1999) suggests shifts in the distribution of sea grasses. Driving factors include temperature stress (and its effects on reproduction), eutrophication, and the frequency of extreme weather events. Changing water depths redistribute habitats (zonation); change in salinity affects physiology and reproduction in sea grasses. Increased disease activity is anticipated, as is shifting competition between sea grass and algae, with the advantage going to the sea grasses.

Short and Neckles (1999) also anticipate synergistic effects: the outcome of the physical changes under global change will be complicated by interactions among biological and physical factors. For example, there is a strong interaction between temperature and CO2 effects on calcification (the impact is greater at warmer temperatures and there is a threshold). Interactions with anthropogenic factors (overfishing, pollution) will be more easily managed.

Changes in the Mediterranean Sea have been studied by United Nations teams (UNEP-MAP-RAC/SPA, 2008). Globally, the anticipated extinction rate of species in the Mediterranean is about 15-37% by 2050. There are some observed species shifts: Sardinella, barracudas, and coryphenes are moving north in fisheries quantities; but sprat and anchovy (small pelagics) have collapsed and tuna and amberjack have changed in their distributions. Lessepsian migrants (Galil, 2007) are on the increase in the eastern Mediterranean. Heat stress is killing sponges and gorgonians, with crashes in extremely hot spells in 1999 and 2003. Heat has also been found to trigger virulence of Vibrio pathogens in sponges, cnidaria, and echnoderms; apparently by inhibition of defense mechanisms of individuals subjected to heat stress.

2.2. CORAL REEFS AND MACROALGAE

Changes in pH, CO2, and calcium carbonate saturation state will have biggest impacts on corals, and crustose and upright calcareous macroalgae. This may shift the balance in favor of turf algae over corals. Increase of CO2 may not only reduce calcification but ultimately dissolve calcified skeletons (Diaz-Pulido et al., 2007).

The second and more obvious impact on coral reefs comes when acidification is combined with higher sea surface temperatures. Elevated sea temperatures as small as 1°C above summer average can lead to bleaching (loss of coral algal symbiotic zooxanthellae following chronic photoinhibition). After bleaching of coral occurs, acidification of water slows recovery. It is recognized that skeleton producing corals grown in acidified experimental conditions can persist and reproduce in a sea anemone-like form, and then revert to skeleton building when the conditions permit (Fine and Tchernov, 2007). However, according to some projections, by 2050, oceans may become too acidic for corals to calcify (Caldeira and Wickett, 2003; Hoegh-Guldberg, 2005; Orr et al., 2005).

Corals are expected to become increasingly rare on reef systems, resulting in less diverse reef communities (Hoegh-Guldberg et al., 2007). Carbonate reef structures will fail to be maintained. Compounded by local stresses, functional collapse of reef systems is anticipated in some locations. This has consequences for other habitats (Hoegh-Guldberg, 1999). Coral reefs protect coastlines from storm damage, erosion, and flooding. The protection they afford enables the development of mangrove swamps and sea grass beds. As coral reefs fail, all these services will decline.

One of the anticipated effects of coral bleaching is increased substrate availability for algal turf, upright macroalgae, and crustose calcareous algae (Diaz-Pulido et al., 2007). This may be balanced by their vulnerability to terrestrial nutrient and sediment input, which may increase with erosion and desertification. Turf algae are expected to be the best competitors for the newly open spaces.

2.3. MARINE ALGAE

A summary of macroalgae response to anticipated climate change shows both positive and negative responses for nearly every climatic stress: change in ocean circulation, increased water temperature, increased CO2, acidification, increased light and UV, sea-level rise, tropical storms, terrestrial inputs, and increased substrate availability (Diaz-Pulido et al., 2007). Algal turfs have predominantly positive response; upright macroalgae are balanced between positive and negative responses, and crustose calcareous algae, like coral, tended to have negative responses.

The direct impact of global climatic thermal rise is presumed minor due to wide temperature tolerance of macroalgae, but the high diversity of macroalgae species makes net response unpredictable. Higher temperatures may enhance turf algae as opposed to fleshy algae.

3. Recommended Conservation Measures

The general strategy for marine conservation under global climate change is best expressed by the United Nations study of the Mediterranean:

At the end of this study, it is necessary to remember that climate change and its effects are irremediable processes. In the long term, the major issue will probably be no more than successfully predicting the future of Mediterranean biodiversity, the future composition of the fisheries and the underwater landscapes, and adapting our ways of using them accordingly. (UNEP-MAP-RAC/SPA, 2008)!

The essentially irreversible nature of global climate change has been suspected for a long time; only the magnitude of change has been questioned. Hence, conservation strategies have largely focused on amelioration of global climate changes and their effects, rather than efforts to reverse them.

So far, amelioration suggestions are sparse. In general, there are no suggestions that the direct effects of global climate change can be reversed. Instead, the suggestions are to increase system resilience by (1) reducing other stresses (such as overfishing) and (2) develop corridors and refuges for restocking.

3.1. COASTAL AREAS

Since global climate change is essentially irreversible in practice, mitigation strategies are necessary in coastal marine systems (Harley et al., 2006). Among the recommendations:

(a) Marine protected areas and no-take reserves, based on known spatial and temporal refuges that can act as buffers against climate-related stress

(b) Fisheries management

(c) Prioritization of key species (by functional role in marine communities)

3.2. MEDITERRANEAN

UNEP-MAP-RAC/SPA (2008): Conservation measures in the Mediterranean mostly focus on improving adaptability (resilience) following the model of Hulme

(2005). Specific recommendations include:

(a) Widen the knowledge base about anticipated impact of global climate change on species and communities to rising temperature, rising sea level, changing rainfall regimes (river spates), increased solar radiation, modification of currents, and changes in biogeochemistry (e.g. pH).

(b) Epidemiological studies. Changing disease patterns is an anticipated concern (see also Harvell et al., 1999).

(c) Develop predictive modeling.

(d) Build federal programs.

(e) Develop economic indicators: what is the cost of global climate change and of conservation?

(f) Assist developing countries in order to assess their vulnerability.

(g) Good ecological engineering. Adaptations of infrastructure to global climate change tend to counter biodiversity conservation choices.

(h) Adapt and change fisheries patterns.

(i) Possibly implement transplantation if species decline locally.

(j) Eliminate other sources of disturbance and stress (pollutants, invaders).

(k) Enhance connectivity for refuges and restocking.

(l) Work on the scale of the whole Mediterranean basin.

(m) Protect relict, non-impacted systems by reserves.

On its web site, the Nature Conservancy organization (TNC) has outlined its conservation strategies with respect to climate change and its impact on marine protected areas (see www.nature.org/initiatives/marine/strategies/art12286.html).

Much of the TNC focus is on coral reefs. Nature Conservancy strategies include locating areas where marine life resists bleaching and creating networks of protected areas to help nearby degraded areas to recover. Much of the strategy is to identify areas where marine life, including corals, seems relatively resistant to damage and focus on conserving these areas as refuges. In the case of coral reefs, connectivity is a consideration, with networks of protected areas allowing one area to provide colonizers to another if it should become degraded.

3.4. COASTAL MANGROVE WETLANDS

It is estimated that between human reclamation of coastal wetlands and rising sea levels due to global climatic change, by 2080 we will have lost about 80% of the world's coastal wetlands. TNC also has a focus on managing mangroves for resilience to climate change (McLeod and Salm, 2006). Most of the strategies are expected: protect coastal mangroves from other anthropogenic stressors to enhance their resilience, maintain buffer zones, restore areas with good prospects, maintain connectivity, develop adaptive management strategies, etc.

3.5. MACROALGAE

Management recommendations are mainly due to concern about expansion of algal turf, rather than loss of macroalgal cover or species. The first recommendation is to protect populations of algal herbivores, then to minimize terrestrial runoff and other sources of nutrient, sediment, and toxicant pollution. Protection of corals will also reduce expansion of macroalgae (Diaz-Pulido et al., 2007).

4. Summary

In general, the situation of marine environments under global climate change looks very bad. The factors anticipated to cause the most change in the marine environment (e.g. sea-temperature and sea-level rises) are also those least likely to be affected by amelioration, and should be seen as permanent, irreversible ch

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