Náttúrufræðingurinn - 1955, Síða 78

184
NÁTTÚRUFRÆÐINGURINN
sunnar dró. Telur Finnur nokkurn veginn öruggt, að nákuðungur hafi
ekki verið kominn suður að Bæ 1940. Árið 1952 fann Finnur lifandi
nákuðung við Skagaströnd.
Nákuðungur er því aftur kominn á þær stöðvar, sem hann þreifst
svo vel á í steinaldarlokin og á bronsöld, en yfirgaf að líkindum í hyrj-
un járnaldar, og óvíst, að hann hafi komið þangað nokkurn tíma
síðar, fyrr en nú.
Þótt talið sé, að nákuðungurinn dreifist ekki sem svif á lirfustigi,
virðist mér augljóst, að þessi afturkoma hans sé afleiðing þeirrar
loftslagsbreytingar siðustu áratuga, sem gerir nú æ meira vart við sig
í fugla- og sædýralífi fslands. Hefur Finnur Guðmundsson í ágætri
ritgerð skýr’t frá breytingum á fuglalífi landsins, en breytingar á sæ-
dýralífi eru aðeins að litlu leyti rannsakaðar, og er það þó merkilegt
rannsóknarefni.
SUMMARY
The Nucella sliore line at Húnaflói in tlie light of tepliro-
chronological and radiocarbon datings,
by Sigurdur Thorarinsson.
In papers published in 1906 and 1910 (cf. the List of References) G. G. Bárdarson
proved a subsidence, the so-called Purpura subsidence, ot have taken place at Húna-
flói in Northern Iceland after the sea level had sunk at least 2 m below the
present level. During the maximum of this subsidence the shore line was about
4 m higher and the sea temperature somewhat higher than now as shown i. a. by the
ample occurrence of the mollusc Nucella (Purpura) lapillus (L.) which at Bárdar-
son’s time did not live on the coasts of Húnaflói, but was found on the S and W
coasts of Iceland. Fig. 1 shows Bárdarson’s diagram of late- postglacical shore line
development at Húnaflói. It has no time scale, as Bárdarson had no means of
establishing such a scale. He, however, suggested that his Purpura subsidence was
probably of the same age as the upper layer of birch trunks in the peat bogs of
the Húnaflói region.
In 1952 the present writer measured a section through the Nucella bar at
Bæjará in Hrútafjördur, the locality most thoroughly investigated by Bárdarson, in
order to establish the age of the subsidence by the tephrochronological method.
Fig. 2 shows the section (cf. also Fig. 3) from which the writer concludes that
the Nucella bar reached its maximum height hardly less than 100—200 years
before the deposition of the Hekla tephra layer H4, and hardly more than 500
years before its deposition. Since then the Hekla tephra layers H3, H4 and H5
— the age of which had previously been estimated as respectively 2500—3000, c.
4000 and 7000—8000 years — have been radiocarbon dated by tho Geochronometric
Laboratory of Yale University (H3) and the Carbon-14 Dating I aboratory, Copen-
hagen (cf. Fig. 5). According to these datings the age of the maximum of the
Purpura subsidence should be 4000—4400 years, probably nearer the higher