(Updates with trade volume, biggest losses; adds bonds, peso)
BUENOS AIRES, Dec 22 (Reuters) - Argentine stocks closed 4.59 percent lower on Monday in thin trade, tracking losses in other bourses amid global economic worries, traders said.
The benchmark MerVal index .MERV ended down at 1,045.56 points in a third session of losses after two weeks of gains. The index has shed 51.4 percent since the start of the year due to the impact of a global financial crisis.
Trade volume was paltry at $8.3 million. Of active issues 6 advanced, 32 declined and 11 were unchanged.
"Profit-taking continued in global markets and our market followed the same trend," said Hernan Labrone, an analyst at Fenix Compania Financiera.
Losses were led by energy-related companies such as Brazil's Petrobras APBR.BA (PETR4.SA), which fell 7.4 percent to 38.60 pesos a share in Buenos Aires, and steel-tube maker Tenaris (TENA.BA) (TS.N), whose shares fell 6.25 percent to 34.50 pesos.
Tenaris, the most heavily weighted company on the MerVal, is a leading supplier of steel pipes to the energy industry.
On the local market, sovereign bonds gained for a fourth consecutive session in over-the-counter trade, rising 0.5 percent on average with the 2038 Par bond in dollars ARPARD=RASL up 2.8 percent to an ask price of 18.20.
Traders said institutional investors are looking to seek high returns after fleeing Argentine debt in October when the government said it would nationalize the private pension fund system, heightening fears it would not be able to service its debt next year.
On the foreign exchange market, the peso closed mixed, weakening 0.22 percent to 3.4225/3.4250 per U.S. dollar in formal interbank trade ARS=RASL.
In informal trade between foreign exchange houses, as measured by Reuters, the peso firmed 0.29 percent to 3.455/3.460 per dollar ARSB=. (Reporting by Walter Bianchi and Jorge Otaola; Writing by Hilary Burke, Editing by Chizu Nomiyama)